VALVE the magazine of astounding sound Buddha extreme FM-3 mod Boulders a turntable odyssey, part two Doc B.C4S’ing the S.E.X. amp Epstein a visit with Fi’s Don Garber Brainiac heavy metal volume 6 number 1 1999 Doc B. 1998 Paraglow a sonic masterpiece by Electronic Tonalities VALVE the magazine of astounding sound Editor and Publisher Dan “Dr. Bottlehead” Schmalle Chief Administrator “Queen Eileen” Schmalle Resident Smart Guy and Technical Editor Paul “Braniac” Joppa Graphic Design Bruce “Papa” Borley Resident Hot Iron and Dr. B’s Bodyguard John “Smoothplate” Tucker Big gun OEM advisor Michael “Airgap” LaFevre Guru’s guru John “Buddha” Camille Contributing Editors David “Full Track” Dintenfass “Crazy Eric” Lenius Our mailing address: VALVE P.O. Box 2786 Poulsbo, WA 98370 by phone: 360-697-1936 business hours: 9-5 PST, Mon -Fri fax: 360-697-3348 e-mail - [email protected] website - http://www.bottlehead.com VALVE in no way assumes responsibility for anyone harming themselves through exposure to the contents of this magazine. W e believe electrons flow from minus to plus, and that they can kill you along the way if you’re not careful. Vacuum tube audio equipment operates at potentially lethal voltages. Always treat it with respect. Many ideas published in this magazine are untried, and involve the use of potentially dangerous parts and tools. In attempting any idea or project published herein, you assume total responsibility for your actions and any harm caused to yourself or others. Please, be careful! This publication is produced as a service to the audio community and is wholly owned and published by Electronic Tonalities. The intent of this publication is to offer ideas to inspire and educate audiophiles in an effort to increase their understanding of the audio equipment they use and cherish. Blatant copying of the circuits published in this magazine for use in commercial products shows a complete lack of original thought. editor’s thing Once again we greet you in a new format, as we have upon occasion over the years (has it been five already?!). Time and technology march on, and we flounder to keep up. Welcome to the first edition of the new electronically published VALVE. The magazine has been produced with the intention that it will print well, and we encourage you to try printing a hard copy from the .PDF file. We had hoped to continue to be able to put out VALVE in both electronic and hardcopy formats, but costs have been rising and we just can’t handle the expense involved in putting out printed issues of VALVE anymore. But- on the bright side, subscriptions are a thing of the past. VALVE will appear each month, downloadable for free at bottlehead.com. Yup, for free. Along with creating a new downloadable issues throughout the year, we will be changing the way we package our back issues. We have been taking a great deal of time to scan and convert our oldest issues, which were pasted up in the traditional fashion, and also to convert our later electronically published issues all into Acrobat .PDF format. We hope to have them all available on CD-ROMs in the next month or so. The 1999 issues will also be available on CD ROM in December of 1999, in case you miss any issues before they are taken down from bottlehead.com and replaced by a new issue during the year. What else is new for 99? A new website look - hopefully on your way to finding this issue you found our new website. After doing a nice job of getting bottlehead.com up and running, Dave Stagner has handed the reins over to my fatherin-law, Bruce Borley. Bruce has many years of experi- ence as a graphic designer, and consequently we will be getting a pretty hip makeover as the months progress. New digs - we’re outgrowing our disorganized “home orifice”setup that we’ve been working in for the past seven years, and this year we will being remodeling to make us more efficient. The ol’ basement workshop will be revamped to include the office that up to now has taken over our family room and also a new kit packing facility. And thanks to a wonderful Xmas gift of cash from the local VALVE members, instigated by Richard Riley and Paul Joppa, we will begin construction on our long awaited new listening room, to be built in the free standing 12’x20’ garage that has been the recycling receptacle at Bottlehead ranch for the last 12 years. Thanks again for your generosity guys, Paul was tickled to see that for the first time since he’s known me I was speechless. Bottlehead is taking trips to the recycle center daily and he’s almost found the garage floor. We’ll cover the adventure of putting this thing together in future issues. Don’t let the blue smoke out, Doc B. on the cover Ray Kuehlthau sent us this photo of his latest woody maker, a two chassis amp based on the now famous Single Ended Direct Coupled Active Loaded Parallel Feed 45 amp from October ‘97 VALVE. This two chassis stunner features carbon fiber chassis plates, zebrawood bases, brass bottom plates, MagneQuest parafeed iron, the brass channel frames of which Ray polished, and the rest of which he shot with faux granite finish. Below is another of Ray’s projects, this one his Paul Joppa 300B S.E.X. amp mod. This guy can crank out gorgeous projects like nobody. New exotica from First Impression Music FIM CD019 Favorite Chinese Instrumentals The Jin Ying Soloists 1 Like Wave Again The Sand (Pipa solo with ensemble) 4:36 2 Singing the Night among Fishing Boats (Jung solo) 4:15 3 Night (Percussion ensemble) 5:54 4 Love Song Of The Grassland (Tung-hsiao with ensemble) 2:34 5 Ducks Quacking (Percussion ensemble) 4:00 6 Love At The Fair (Er-hu solo with ensemble) 5:04 7 The Fishing Song (Bawoo solo with ensemble) 4:53 8 Happy Reunion (Xylophone solo with ensemble) 2:55 9 Chinese Martial Art (Emsemble) 1:43 10 The Flowing Stream (Er-hu solo with Yang chin) 8:25 11 Spenpadei Folksong (Yang-chin solo with ensemble) 4:32 12 Autumn Moon (Er-hu solo with ensemble) 7:06 13 Moonlight Over The Spring River (ensemble) 9:22 14 Variation On Yang City Tune (Ku-jung solo) 5:36 FIM CD020 A Vocal Tribute to Ben Webster Jacintha, Vocal Teddy Edwards, tenor sax; Kei Akagi, piano; Darek Oles, bass; Larance Marable, drums 1 Georgia On My Mind (Gorrell-Carmichael/BMI) 5:19 2 The Look Of Love (Baccharach-David/ASCAP) 4:08 3 Danny Boy (Traditional) 7:26 4 Somewhere Over The Rainbow (Harburg-Allen/ASCAP) 9:43 5 Startdust (Parish-Carmichael/ASCAP) 6:40 6 In The Wee Small Hours Of Morning (Hillard-Mann/ASCAP) 4:15 7 Tenderly (Lawrence-Gross/ ASCAP) 5:25 8 Our Love Is Here To Stay (George & Ira Gershwin/ ASCAP) 3:19 9 How Long Has This Been Going On? (George & Ira Gershwin/ASCAP) 5:28 10 Pennies From Heaven (Burke-Johnston/ ASCAP) 3:12 #189 16149 Redmond Way Redmond, WA 98052 http://www.fimpression.com Tel: 425-868-5326 Fax: 425-836-9061 Buddhafying the Dyna FM-3 By John “Buddha” Camille You guys who know Buddha also know I let a djinni out of the bottle when I asked him for a few simple ideas on modding a little ’ol FM-3. Hang on to your hats with this one bottleheads, by the time Buddha gets through with you, you’ll not only have the meanest FM-3 in town, you’ll have the cleanest tubes too. - Doc B. Dear Dr. R sub g (Rg), Was very amused at the third issue of “V”. Your new subtitle bears out the caliber of your readership. (Buddha is of course referring to the unending string of corrections I got regarding that dumb grid resistor I left on the output tube in the Blues Master article - B.) The FM-3 has turned into a real challenge. My thoughts of hot-rodding the tuner and IF strips were dashed by the wide open construction of the unit. Using higher gm tubes for the mixer and IF strips was not possible due to the lack of shielding. Above a certain total gain point the RF-IF strip takes off and will oscillate at around 1 0 7 MHz, the tenth harmonic of the IF. The feedback path is primarily through radiation from the last IF stage back through the RF stage grid circuit, in concert with direct conduction through the B+ and heater circuits. There is also a lot of direct radiation above chassis from tubes and the mickey mouse tube and IF can shields. This problem prevented me from getting 60 dB plus of limiting on noise alone by using hotter tubes in the IF. I did achieve a happy balance of gains between the RF and IF that permits better limiting, slightly increased total gain, and much better noise figure with the 6DJ8 front end. Several college stations thirty to forty miles way now come in full quieting with a 3 foot clip lead antenna. Eventually I hope to fully shield the RF section and possibly the bottom of the IF with proper interstage shielding and tons of bulkhead feed-throughs. I did cheat and use button mica caps on the RF board while trying to calm oscillations. These caps get the RF off of the lower cathode and upper grid and of course increased RF gain considerably. This required lowering the gain on the IF strip. This was done by lowering plate and screen voltages, which had the added benefit of providing better limiting. Virtually any signal will now produce a limited 4Vpk-pk signal on the plate of V-6. A slight bit of AM’ing is still visible on positive peaks, however. Before modding, AM was significant on both positive and negative peaks. The beast is really starting to sound solid. I have not had time to redo the first audio stage, V-7, and the audio output stage V-72. Plan to use a 5687 for V-7 and 12B4’s for V-72. Of course, C4S’s will be used for cathode and plate follower feedback on the output. Will probably change the volume control to a 6dB stepped attenuator for better high frequency response. The present 19,38 and 67kHz attenuation really sucks. Plan to use plenty of LC traps and filtering here, along with a proper de-emphasis filter. May need a cathode follower to drive these filters properly. The present system has a lot of 38 kHz on the output and tons of 67 kHz SCA on some stations. Hum has always been a problem on my unit. Got rid of about 95% of it with additional filtering and direct wiring the primary power. Putting 120 VAC (to the on-off switch) within 1/2 inch of the first audio stage is not very cool. Am planning to eventually move the power supply off chassis and DC everything in a large audio visual console I had built in the Phillipines back in the 60’s. The wood, Nara, is too hard to work so I’ll have to stick with the heavily modded stuff that will fit the holes on the cabinet work. Tw eaks that m ight be applicable to the ex perim enter RF-IF Tube Shielding The original tube shields are tube killers. I had replaced the tin can shields with IERC style shields when the unit was built back in the early 60’s. All tubes still have plenty of emmision with probably 100K hours of use. These shields are still hot with RF however, as the original ground strip corrodes pretty quick. A better answer is my combination tube shield/microphonic attenuator. This process should be used on all tubes in the set, especially the RF-IF tubes. Some folks might not like the sonics when this technique is used on the audio tubes because much of the reverb is lost... Procedure 1 2 3 Select a new tube that checks way over good. Wire brush pins until shiny with a gun bore brush chucked up in a drill motor or Dremel tool. Practice on an old tube until you figure it out. Wash tube thoroughly with tooth brush and 409. Rinse and blow dry. Do not touch pins with fin- gers again. We’re talking clean room plastic gloves here (food handler gloves are cheaper) 4 Wrap one layer of 1” 3M foil shielding tape around tube and solder the seam in several places. Connect shield to the appropriate pin with 24 ga. wire wrap wire, see figure 1. The RFI tape (Digi-Key 3M1181C) is pretty pricey but will be a lifetime supply for most experimenters. I use tons of it for ground planes, power busses, shielding, etc. The stuff is severly addictive. 5 Clean rosin from all solder points with multiple Q-tips and anhydrous alcohol (Caig Caikleen) or toluene. This process must be repeated several times in order to remove all film traces. 6 Wash tube again with 409 and toothbrush (especially around tube pins). Rinse and blow dry. Blow dry is important in order to prevent leakage from water rings from solutes. Do not try to wipe dry. 7 Mask tube pins (use blue 3M masking tape) and shoot tube with flat black Krylon. The paint and copper drop envelope temperatures, significantly increasing tube life. The glass/adhesive/copper composite reduces microphonic ringing measurably. Note: for those using regular masking tape - clean adhesive off of tube pins with Q-tips saturated with Goof-Off. Then degrease with 409, etc. 8 Chuck one half of a Q-tip in a drill motor and add a small drop of Caig Pro-Gold to the cotton. Use this rotary buffer to polish tube pins. Repest process with clean Qtips until pins produce no more black deposits on cotton. Surprise, surprise, you thought they were clean. Note: A short lead may be soldered to the copper shield and run to the nearest analog ground when all tube pins are floating. Where necessary, a 1/16” hole may be drilled in the chassis for this ground connection. RF-IF and other non-audio signal tube shields may be returned to a chassis mounted solder lug, a ground plane or a ground buss. Make the connection short and sweet. IF Transformer shielding The IF can mounting lugs do not make a serious electrical connection to the aluminum can. All of my cans were initially hot with RF. Physical movement of the can would also produce intermittent contact and detuning of the transformer. The IF transformers were removed for overhaul and clean-up. While I was at it, the winding assemblies were also removed from the cans and the tank capacitors were replaced , and all internal solder joints were sucked dry and resoldered. Several joints looked suspicious where the magnet wire insulation had not been volitized completely. In addition, several windings had broken loose from the wax tie down process. The wax was removed with a slightly warm solder iron tip and the wire was rewound in place and recoated with the wax removed previously. The warm solder iron can be used to remelt the wax blob onto the winding and the coil former. A step by step follows: 12 1 2 3 4 5 6 7 8 9 10 11 Witness mark IF cans and circuit board with a scratch awl.prior to removal. The green alignment mark will go away later. Early cans had a slot punched into the top of the can and this will suffice. Remove solder from board with solder sucker (6 places) and gently rock the can ‘around the clock’ as joints are heated in succession until the can is free. Witness mark the can and the coil assembly. A green dot may or may not still exist an the winding frame as an alignment marker, just make sure you get it right. For those who are reading the instructions after the fact, the primary winding is on the bottom next to the tank capacitors, see schematic symbology. Number each can in accordance with its circuit location with the scratch awl, i.e., T-1 would be numbered 43201-1, T-2 would be dash 2, etc. Flatten the four coil frame mounting indentations in the can with the needle nose pliers and gently remove the winding assembly from the can. Done right, the winding can be pulled out with finger pressure. Don’t grip the solder lugs with pliers and pull or you may have a real fabrication problem - the plastic frame is brittle. Polish the can with 409 and a piece of 3M Scotchbrite. The tin plated steel mounting lugs should be brite for later soldering. rinse and blow dry. Wrap one turn of 1/2” wide copper tape around the can so that approximately 1/2 of the mounting lug is covered. Solder the copper to both lugs and tack the top of the seam, see figure 2. Remove rosin from solder joints and degrease with 409. Rinse and blow dry. Shoot can with Krylon to forstall galvanic action. Flat black is best for tube life. Clip out the 22 pf disc capacitor from the primary side of the transformer (lower winding) and replace with a 22 pF/N750 disc ceramic, DIGI-KEY 1305PH. When soldering the new part into the circuit, first wrap the leads around the solder joints for the coils leads. This technique will possibly solve a bad joint existant since the original manufacture. Remove iron as soon as the solder flows as the coil frame plastic is pretty poor. Clip out the 10pF disc capacitor attached to the secondary terminals. Replace with a Phillips 10 pF /N750 disc DIGI-KEY 1301PH observing the above cautions. 13 14 15 16 17 Measure coil resistance after modification. Proper primary resistance is ~0.75Ω and the secondary resistance is ~ 0.78Ω. Align witness marks on the IF can and the coil assembly and insert coil assembly into the can. Insure coil form is fully seated in the circular boss on the top of the can. Use awl to indent the can back into the grooves in the coil assembly base frame (four places). Place 0.1 in. length of small teflon tubing or wire insulation over pins 2 and 4 of the IF can. Drill clearance holes in PC boards at the pins 2 and 4 locations for the above teflon insulation. (typical 1/16” - 2 places per transformer). New wiring will lift RF hot wiring off the lossy PC board material Strip PC board solder pads arpund these holes and lift trace off board back to the plate or coupling cap solder pad. Apply soldering iron to the plate lead or coupling cap and they may be lifted off the board in one fell swoop. The idea is to get as much of these RF leads as possible off the crummy board material and build a decent Rf transmission line. See fig. 3. Another aim is to reduce circuit “Q” and widen bandwidth. The direct wiring spec’d also reduces radiation ef- fects. Tube Sockets The tubes sockets used in the FM-3 are a disaster. Each socket required a half dozen round toothpicks dipped in Pro-Gold to remove corrosion, etc. Twirl the picks in the pin contacts until they come away clean Grounding Tuning Cap Shaft The tuning shaft is fairly hot with RF and needs to be positively grounded. I used the old ham radio trick of fabbing a clockwork spring buss between the shaft and the shield. The shield around the variable cap also needs to be tack soldered to the chassis every inch. This process is fairly easy when the filter cap (C-32) is replaced. See next page. RF Frequency Shift Joe Roberts mentioned that the FM-3 is well known for tuning instability, something I have never encountered. Having done a lot of VHF/UHF work, I’ve always been amazed how stable the thing is. Well, the palmprint on the forehead occured when thumbing these since some are 2pF feedthrus for signal leads most are 470 to 1500 pF for power leads and bypasses. Other mods 1 2 3 the through the assembly manual and seeing the “real” C-8. I had replaced the cheapass ceramic trimmer with a Johanson air variable when I built the thing, so I had experienced no problems. Digi-Key carries the Sprague-Goodman line of trimmer caps that should work well. I used a style 9, 1-10pF cap. pn SG4004. Looks like a good fit. Surplus is better. This type of cap, along with the button mica feedthrus, can be found in those old RF assemblies sold by the pound at the flea market. I paid 50 cents for a filter box that contained 8 sapphire insulated Johansons about a year ago. Samo, samo on bulkhead, ceramic, feedthrus such as the SCI’s sold by Newark, p 151. Old TV tuners that sell for a buck or two are usually filled with feedthrus. Will need a capacitance checker with 4 The HP 5082-2810 diodes also work well for the demultiplex circuit and they are a helluvalot easier to match. I am going to put the 47K resistors and the diodes in the can for T-73. Leads are too long the way they are presently scattered over the PC board. The whole de-mux board needs to be replaced with an FR-4 proto board with ground plane. Will probably steal the design for a good de-mux from a Fisher or something highly acclaimed. Might move V-7 over to the de-mux board and put the whole thing in a die-cast box. You are right getting rid of the six for a nickel parts on the rear deck.(I suggested getting rid of the crummy antenna connector screws and installing a nice F connector - B.) I am going to BNC on audio stuff. Well, enough B.S. for a while - Brainiac’s Heavy Metal ably use a 6J5 or 6SN7 or 12AU7 tube in single ended drive at reasonable current. sidual ringing at around 250kHz - not bad at all! Both sides are -1dB at 10kHz; they are down 3dB at 25 and 28kHz. Bass extends to -1dB at 45 Hz, 3dB at 20 Hz with small signals (7 volts rms) This one is in a U-channel frame, with a lamination stack of 1.875 by 1.5 by 0.625 inch and mounting holes 2 3/8 inches apart. It weighs 8 oz. on my kitchen scale. ...an occasional review of some nifty chunk of iron (usually cheap!) Low frequency data: Today’s Topic: the Allied “Ally” interstage transformer single-ended Turns ratio: OK, so I couldn’t think of a clever name for this one! If you have a better name, let me know! Primary: Secondary: DC current: This unit is available for $15 from Allied Radio, and is one of the small class of cheap interstage units available. There are several in the $10 to $20 range, made for old radios usually. Nothing fancy, but their small size makes for low leakage inductance even without interleaving and they can sometimes be used with decent results. They are usually designed for SE drive of push-pull output tubes, so they are not optimum for single-ended output. In my experience these transformers are often very inaccurate in their specifications; they should be measured before a circuit is designed around them. This one is attractive because it operates at a relatively high impedance level. It can comfort- Peak output: 1:1CT; specified for 10k:10kCT impedance 1240 ohm DC 798+731 ohm DC Inductance with 12v/ 60Hz excitation is 44H at 0v, falling to 22H at 24mA. I would rate it at 12mA, where inductance is 35H 52.5v + 52.5v at 40 Hz. High frequency data (resistances for a decent-looking square ware at 5kHz) push-pull: Source impedance 8k plus a load impedance of 12k + 12k leaves only a tiny re- Seems to work best with 8k source and a 15k load endto-end. It’s -1dB from 45Hz to 11kHz; -3dB at 20Hz and 20kHz. Not as good as push-pull, but not terrible either. This is pretty decent performance, considering the price. It could, just barely, drive a pair of 2A3’s in pushpull. The fact that it could do so with a 56 as driver is attractive, though another gain stage would be needed for any reasonable sensitivity. The relatively high impedance and decent current handling means the driver can operate at reasonable voltages, as much as 300400v, something other interstage transformers have a hard time with. Paul Joppa ActiveS.E.X. 6Kohm 3W Camille Cascode Constant Current Source (C4S) R1 = 0.95V/Iplate R2 = Vtop of load/.002mA 300VDC R1 60 ohm 1/4W 47 mfd 450V Remove 1K WW resistor from power supply. Replace second 10 mfd filter 410VDC capacitor with a 47 mfd @ 450V electrolytic capacitor original SEX OPT as plate choke MPS4250 or 2N2907 3mfd 630VDC MJE 350 R2 3 series 50K ohm 1W paralleled 6DN7 triodes no.2 2mA 250VDC paralleled 6DN7 triodes no.1 .47 mfd 630VDC 270K 1/4W 100K 1/4W A C4S adaptation for the S.E.X. amd ParaS.E.X. kits By Doc B. 8VDC 1Kohm 1/4W 16mA new SEX parafeed OPT 220mfd 35V orange 220mfd 35V 390 ohms 2W green Fi‘n’ Art by Jeremy Epstein Don Garber, the man behind the Fi amplifier company, has an enviable life. Ensconced in a commodious hundred-and-fifty-year-old Brooklyn carriage house, Don paints abstract paintings and builds a unique line of bottle-driven audio equipment. He has the good fortune to be supervised by Max, his shaggy big dog, and inspired by Ikuyo, his muse, who was responsible for my visit. My wife was talking to Ikuyo, Don’s wife, at a party a few months ago. She came and told me, “Ikie’s husband builds tube audio gear like that stuff you’re into.” I explained to Don that I was a neophyte bottlehead, and he was very kind. Later, I checked up on Fi and quickly learned that my neighbor was responsible for some of the most interesting wattage-challenged gear around, and that he had been a pioneer in the emergence of triodemania here in the US. So I imposed on his hospitality and invited myself over to see what a real professional amp builder looks like. Piled neatly in the Fi production space were dozens of chassis plates, which Don had just finished drilling for the next batch of amps. Trannies and tubes were stacked in neat little rows and aluminum sawdust was everywhere. While Don chooses his parts with deliberate care, according to quality, price, and their synergy with the circuit application, he doesn’t seem to me to be using anything wildly esoteric or mysterious. Since he builds in small quantities, he gets his parts in reasonably-sized batches : there were no tell-tale crates revealing bargain bulk sourcing. I buy my parts from some of the same places Don does. Most of the tubes he uses are current production. About the only evidence of a tweaky mentality I saw was the silver wire used inside the amps, hardly voodoo. And Don admits, “I’m no great audio designer, and I don’t want to contend that I am. I guess I’ve looked at a lot of things, tried a lot of things. My approach is more empirical than anything else.” What he shoots for is simplicity, value, precise workmanship and a clean look. He doesn’t much like talking about audio, and hype is notDon’s style. It’s an awful lot easier to get him talking about music. ”I’ve been struck by audiophiles in general, (I tend to think my customers are a little better than most, or is that just my own ego in there?) the music they listen to - you’ll try to get past my snobbishness - is such trash! But most of them, it’s just to demonstrate their systems. And I find that this tends to be less true among people that build their own stuff. You would think it might be the other way around but it’s not.” Don and his wife regularly calibrate their ears by attending chamber concerts at Bargemusic, a floating concert space moored under the Brooklyn Bridge. A window onto the lower Manhattan skyline forms a spectacular backdrop for the world-class musicians who perform there. Perhaps it’s his experience dealing with the audio salon crowd (Fi was started partly to feed product into a retail store of the same name Don ran a while back) but Don Garber is no fussbudget. When I arrived at his shop/soundroom he methodically set up his wonderful 2A3 monoblocks to drive Exemplar horns with zip cord (Yo, Don, Smoothplate’s gonna crap his pants when he reads this -B.), no-name interconnects, and a little beer. Carefully, he tuned the room by moving a pile of cardboard boxes out from in front of the right speaker, and powerline conditioning was taken care of by a 50' orange extension cord and some cheater plugs. Together we listened to some mutual favorites, like the new Dylan live set and Lucinda Williams’ long-awaited new album, and I turned him on to the terrific guitar Goldberg Variations by Kurt Rodarmer. We talked about a lot of things : Brooklyn real estate, family, slide guitar, and even the business of audio. Neither one of us was unduly bothered by the cheap interconnects, let’s just say, and my cassette of our interview has the same relaxed, open, effortless sound as the original playback. At one point, Don commented, “I can get into a discussion about a specific thing or a specific problem or approach to something and do that, but the ‘audio bullshit session’ just kind of drives me up a wall.” So I shut up and listened a bit closer. I heard an awful lot of music coming out of Don’s system, both with the 300B X3 and the monoblock 2A3 amps : we listened to different styles of music on each but I preferred the 2A3’s and Don concurred. He said, “The 2A3 amps are the better amp, but you have to compare them on a level playing field. These speakers are efficient enough that it truly is a fair comparison, but if you get, say, a pair of Spendors, and you play the 300B’s with them, they do this” - and he proceeded to caricature the stance of a pumped-up muscle guy. Don has enjoyed some attention with his recent new product, a stereo 2A3 amplifier named the X. “I wanted to build the cheapest good 2A3 amp that I could. There were a lot of people that wanted to buy one and couldn’t afford it.” He has done that and more. The X features a chassis in the shape of an extruded letter “x” standing on its end. It looks a little like a tank trap with tubes and transformers peeking out of various planes. I doubt I am the first to predict that the Fi X will someday be in the permanent design collection of the Museum of Modern Art. Its construction literally turns amp design on its ear. The X arrangement is more than just startlingly cool, though : it provides physical isolation between power supply and audio circuitry, permits excellent ventilation, and cuts the audio signal path shorter than a New York minute. He has built on the novel X with two new products : the Y line stage and the X3, a 300B stereo power amp. I asked Don how he thought up the X chassis concept, and he said, “I’d been thinking of doing a cheap version of the 2A3 amp for a long time and I knew partswise what to do, how to keep the price way down. But I didn’t want to put it on a little Bud-box chassis, because then it would look just like every other cheap little amp. I tried this idea and that idea, with the idea of keeping the power supply and the amp seperate. I didn’t come up with anything that was any good at all. I was riding the subway one day, when I was just . . . there it was!” He smiles and his fingers make a little “x” as the words trail off. “I quickly sketched it on newspaper, came home, figured it out, and everything just fell into place. It worked perfectly. I’m not sure how it happened, it was just one of those inspirations that happens.” It looked like his amplifier brainstorm went on to inspire a painting : hanging on the wall was a bichromatic canvas with cornerto-corner diagonal elements. He was clearly proud of another creation : an elegant WE 421Astereo amp sporting only a dual triode driver, the dual triode power tube, and a rectifier nestled amidst big iron. He took it down off a shelf to show me. “This was the first one to use the multiple levels of chassis plates,” the signature style of the earlier Fi amps. He showed me how the design inherently shields and physically isolates the audio path from the power supply. Naturally, it also looks very stylish. Here is a man whose products embody modern industrial design, who paints in a clean, abstract style, and yet spent about a half hour lovingly displaying some of his antique tubes, including the bizzarre 316A, which looks like a tiny weathervane inside the brain of Rosie, the Jetsons’ robot maid. Like his 3-tube stereo amp, Don Garber may look simple but he works on many levels. While Don has been refining his taste in circuitry for decades now, he allows room for improvement : “Somebody said I got to the point where I kept taking things out until it stopped working. And then put that part back in, and that was it. Not quite, but almost. From what I hear, simpler is usually better. Now you could make that into a ‘rule,’ and go and carve it into a beam up over your shop. But then tomorrow you might find out that you’re wrong, so I don’t like to get into making rules. As soon as you make something into a rule, you close doors.” Doing that may make your life simpler, but . . .” Don’s affection for simplicity is reflected in his preference for direct-coupled circuits. When we were discussing some of the tradeoffs in designing the inexpensive X, Don pointed out that a direct-coupled design is more forgiving of LF limitations in the output transformer : there is no rolloff from the coupling cap to exacerbate any bottom-end phase shift in the transformer. While the original (2A3) X is direct-coupled, he was clearly disappointed that he could not direct-couple the new 300B version and still make it work in the X chassis. The more complicated power supply also would have driven the price of the X3 too high to fit in with the conception of the X as an affordable product. I wouldn’t be surprised if an all-directcoupled 300B amp comes out of Fi in the near future : Don has a pretty clear idea in mind of how he wants one built. Also in his plans : a phono stage for the Y preamp, and experimenting with the sound of the beefy KR 2A3 when run at a higher dissipation. Don’s curious, though he’s not sure a move up to six watts will be worthwhile. The remarkably musical 2A3 sound may or may not show up using that operating point, he suspects, and also he’s not sure a six-watt amplifier compliments many more speakers than a three-watt amp does. Garber is the easternmost member of the “Audio Dream Team,” in charge of chassis and layout for the upcoming hush-hush project soon to come out of Area 51 in the Mojave desert. Parallel-fed, active-loaded, transformer-coupled, this X-wing fighter is going to pack a fair amount of iron on whatever chassis Don comes up with. I joked with him about a Kustom Kandy Kolor for such a hot rod, and he scowled. (Don scowls a lot.) “I like things to look like what they are. If it’s metal, it should look like metal.” Later on, he pointed out a small cosmetic flaw in a transformer prototype he had rejected for other reasons. Clearly, this is a picky guy with strong opinions about how his equipment looks as well as how it sounds. I asked Don if he thought the work he puts into his gear satisfies the side of his soul that is also a fine artist. “It’s nothing like painting, that’s a totally different thing. I’ve read people talking about, building amps and so forth is an art of its own. No. No, it’s craft.” He pointed towards the speaker, from which played a legendary live recording by another cranky master. “What’s coming out of that, that is the art.” I hope Don Garber gets the satisfaction someday of seeing his paintings hanging in a museum. But painting is a crowded, competitive field, and many who excel are never recognized. He may have to settle for seeing his X amp on a pedestal - it’s a shoo-in. Re : the schematic. Don said, “I wish I had priced the X at $892.00 instead of $895.00.” I asked why. “So it would be exactly 1/ 100th of the price of the Ongaku. W henever you hear, ‘cost-no-object,’ cost IS the object”. X da’ basics job is a done deal. What do those stripes on the resistors mean? Improving our soldering skills by Doc B. Here’s a little reparte I had with a novice Foreplay customer a while back after helping him get his Foreplay up and running by resoldering all the joints: I practiced soldering with my sca-35 and replaced some its dried up wires and got that working. That was my first solder experience. I guess I will solder next time by heating up the end device first, say a lead or terminal connection then try to get the solder on top of the wire and then apply tip to the solder. The trick is to get the tip of the iron in such a position that it heats both the wire and the terminal it is being attached to at the same time. This is critical, otherwise the solder may only adhere to the one surface that’s hottest. You should get both the wire and terminal hot enough that you will melt and flow the solder when it is applied to the joint itself, not the tip of the iron. If this creates a non shiny solder then should I reheat the connection until it hot again and see if that settles it? In general yes, although some of the newer types of solder like the 97% tin /3% copper “lead free” solder I use flashes to a dull finish when cool, even on a perfect joint. The thing to look for is an even coating of solder over both the wire and the terminal, and that the solder has flowed enough to form a more or less concave “fillet” instead of a convex “blob” or ball at the joint. When reheating a joint it is a good practice to add just a bit more solder to the joint, which helps stem the inevitable pull of gravity drawing the remelted original solder down away from the joint. If a joint is already gobbed up with a lot of solder, use solder wick or a desoldering bulb to remove the excess before resoldering the joint. I think I got the basic idea behind it (not the dexterity quite yet) but would appreciate any more soldering tips. Since I want to jump to a 2a3 amp next I dont want to keep on making those errors. Part of the trick is to attach all the wires securely by wrapping them around the terminal before you solder the joint. This frees you from trying to hold the wire in the terminal while soldering, leaving one hand free to hold the iron, and one hand free to apply the solder. Holding a wire in place while soldering is not steady enough, the joint will inevitably crystallize while cooling due to tiny movements in the wire. Make sure the solder gets hot enough to freely flow over and through the joint. The whole joint, all around the terminal, should be penetrated and evenly coated with solder. Using a hot enough iron is important too. Most of the hotshit solderers I know have an assortment of irons. Always included in this assortment is a big ugly 45W55W iron with a big chisel tip. If their fancy little temperature controlled model doesn’t heat a thick joint enough, like say in the case of soldering speaker wire to terminal posts, they bring out the big mutha and the We get a certain number of calls complaining that we don’t hand label each 1/4 watt resistor in our kits. Newsflash, folks. They are already labeled. It’s just a matter of knowing what those little stripes mean. The basic layout used involves four or five stripes. On older style “precision” resistors there are usually four stripes, on newer metal films there are often five to accomodate the hair splitting values available in the 1% types.On either style of resistor all but the last stripe denote number values according to the following plan: black = 0 brown = 1 red = 2 orange = 3 yellow = 4 green = 5 blue = 6 purple = 7 grey = 8 white = 9 On the four stripe variety, the first two numbers denote ordered values. On five stripers, the first three stripes denote ordered values. For example if the first two stripes on a four striper are red, purple, we are looking at 27. The next (second to last) stripe on either value denotes a “power of ten” multiplier. For example, abrown (value 1) stripe denotes that you should multiply the first two (or three) stripes by the factor 101, or ten. So a four stripe resistor with the first three colors of colors red, purple, brown would translate to 27 X 101 = 270 ohms. Red, purple, yellow (value 4) would be 27 x 104 or 270,000 (a.k.a. 270K) ohms, etc. To denote the 270 ohm value on a five striper, the first four stripes would read, red, purple, black, black, which translates to the first three stripes denoting the number 270, and the fourth stripe denoting a multiplication factor of 100, which is of course, one. What about the last stripe? It denotes the tolerance, or accepted plus and minus range of variance of the resistor’s value from that stated by the stripes. Mostly these days we see gold, which denotes a 5% tolerance; red, which denotes a 2% tolerance; and brown, which denotes 1% tolerance. There are other codes not so often seen anymore, unless you are fooling with old carbon composition resistors - silver is 10% tolerance, no stripe is 20% tolerance, and even more obscure, yellow denotes 4% tolerance and orange denotes 3% tolerance. So, you are now thoroughly confused and your middle aged eyes can barely make out the stripe colors anyway? That’s why God invented the volt-ohm meter, homes. Just measure the damned things with the meter set on the “ohms” scale and forget this. experiments with a turntable - part two By Rene Bolders a new platter After the successes mentioned last issue I began to look at the glass platter a little more critically, and I wondered if I could possibly improve here. At that time acrylic platters became very popular in Germany and elsewhere, and since acrylic or Perspex is very close to vinyl materialwise, I felt that it could be a good match. I chose Perspex as a suitable material because it has high density but it is not too hard and is easily machined. I bought a block 14”x14”x3” and started by cutting a rough round disc with a bandsaw. Since I’m a machinist/fabricator by trade, it wasn’t very difficult for me to turn out a nice platter on the lathe. The height is the same as the glass platter since I wanted to do a direct comparison between the glass and Perspex without changing the tonearm height. Well, it was worth the trouble, the acrylic platter produces an overall deeper bass. I feel that the bass and midbass both increased, and the soundstage also seemed to be deeper and more convincing. I tried the two platters back and forth the following days but the acrylic platter was always the clear winner. Weight-wise I didn’t gain or lose anything, important to preserve the bottom bearing load. speed control Next I began to look at the platter speed, because I had noticed for some time that it wasn’t as constant as I’d wished. The little motor is basically a 110 volt motor, 24 pole synchronous type, but it was wired for 230 volts, which means if you look at a stroboscopic disc with a neon light you’ll notice that the little dots or stripes do not stand still, but rather they kind of go forward and backward all the time as if they were vibrating The root problem is that the 24 pole synchro motor gives 24 little jerks in one revolution. This is visible with a good stroboscope. Om top of that the overall speed varies quite a lot depending on the time of day because there is not always 50Hz (or 60Hz in the US) coming out of the wall outlet. I measured and monitored the line voltage and frequency for a couple of days, only to see it fluctuate from 218 volts in daytime to 238 volts at night. the frequency varied from 48 Hz to 53 Hz. This is not a very desirable situation, and in my opinion is audible. My good friend Bernd (still lives in Berlin) came up with a solution. He designed an external power supply circuit board for 110/220V 50/60Hz operation. All I had to do was build a nice enclosure, install a few plugs and rewire the motor to 110V. See the photo showing the power supply sitting next to the turntable. The round thing on top is a record clamp. The power supply generates a precise square wave through a high frequency quartz generator and digital divider. Frequncy can be set for an exact 50Hz or 60Hz. The signal then goes through an active filter and gets converted to a pure sine wave. A nine watt class A amplifier amplifies the sine wave and feeds it straight into the motor. Because the 110V motor was wired to 220V through a voltage divider, I gained some torque as I hooked it back to 110V. This was to my advantage because of the relatively high mass platter. The constant feed of pure 110V 50Hz into the motor independent of mains fluctuations made the motor turn very constant. When I measured the speed with the stroboscope, to my satisfaction the stripes on the disc were nearly standing still. Of course the motor is still a 24 pole synchro motor, but with a clean signal feed it works great. I would describe the advantage of an external power supply to be better control in the bass region, a broader soundstage, and a cleaner sound overall. two steps forward, one step back The next experiment went wrong. I noticed that on Pierre Lerne turntables the surface of the platter is not straight but concave. The reason for this seems to be that the record has good contact with the surface of the platter. The record clamp or weight forces the record to the surface, so even if a record is slightly warped it will still sit solidly on the platter and not “wave” in the air. Some records are concave themselves which results in them siting on the platter either as a “little hill” or when you turn them around as a frisbee up in the air. I know one should try to avoid buying frisbees, we all like 180 gram audiophile virgon vinyl limited series handpicked and so on. But if you like older stuff like me, jazz from the 50’s and 60’s, and you finally find the one record you were looking for for two years, you can’t be picky. You have to find a way to make it work. Thus, following this spirit, I machined the platter slightly concave. I adjusted the cartridge parallel to the platter’s surface to have a good vertical azimuth. First I used a precision ruler to align the cartridge body to the platter and later I checked with a test record (1kHz test tone) and a digital voltmeter for fine tuning. Now all this works great when you play frisbee’s from the 70’s and 80’s, pop music and so on (Dynaflex records work great). But it all starts going wrong when you play LSC’s, Blue Notes, and especially 180 gram pressings, because they don’t give as easily as you would think. Plus, because of the differences in thickness the vertical azimuth changes all the time, which results in decreasing channel separation as well as lost balance and soundstage width. On top of that, when it gets to an extreme one channel plays louder than the other, there is excessive groove wear on one channel and the antiskating is affected.This is all very theoretical, but I still don’t like it. On high quality turntables everything matters and everything is audible. I fought with these problems for a month or two, but then I lost patience and resigned, which resulted in my machining the platter straight and setting the cartridge back to where it was. A nice vacuum hold down might do the job, but I haven’t gotten to this yet. tonearm cable As I mentioned earlier, my turntable came with a Grado Signature Tonearm and Grado interconnects. The interconnects proved to be very good, but they are as old as the turntable itself (15-20 years, who knows?). Through time they may have become corroded or something, anyway I told myself this as an excuse to try something new. I bought van den Hul phono interconnects with a straight DIN-plug and liked them, but only until my friend Bernd suggested trying a Straightwire Microlink cable. I like this cable a lot, in fact I still use it today, it is specially designed for low level analog signals and doesn’t cost a fortune. I’m lured by some of today’s top cables and I shall try to replace the whole cable (including the tonearm, and removing the DIN connection), probably with Kimber Silver, Cardas, or Discovery. cartridge The Grado Signature cartridge installed on the tonearm when I bought the turntable had a bent cantilever. My friend Bernd just happened to have a brand new Benz MC-2 and since the price was right, it went straight under the Grado headshell. The Benz family of cartridges is somewhat of an interesting story. The Benz Company ( from Switzerland) is a manufacturer of high quality cartridges. They design and manufacture cartridges under thier own name as well as producing cartridges for other companies, which sometimes leads to confusion. My cartridge is called the MC-2 (Europe), however kit is called the MC-3 in the US, and is identical or very close to the Madrigal Carnegie 2, Taurus DDT, Empire MC1000, van den Hul MC-10, MC-one, MC-two, Empire MC-2000, and has lots of similarities with some Ortofon units. This is not to say a bad word about Benz & Co., but rather to take some of the hype out of cartridges. The same goes for Scan-Tech of Japan, who also make a whole range cartridges under different names. The Koetsu is very sensitive to all parameters. After much trying and experimenting I ended up with a VTA of 25 degrees, tracking force of 2.0 grams, 47Kohm loading and a 100 pF cap. The difference between 1.8 grm and 2.0 gram tracking is very audible. It’s fun to experiment with this Koetsu because when everything is right it really sings. tonearm All this experimenting led to modification of the Grado tonearm. It’s Grado’s approach to not use only gravity or only spring force to adjust tracking force, but rather both. For 1-1/2 grams of tracking force, the setup uses 1 gram of gravitational load and 1/2 gram of spring While my cartridge was at the factory I still wanted to play records, so I checked out my friend Bernd’s collection to see what he had that I might like. As it happened a Koetsu Black Magic Gold had just arrived from van den Hul where it was serviced and retipped. I purchased it on the spot and it really made me happy, in fact I still use it today. There is something special about Koetsus. I heard a Koetsu Rosewood on Bernd’s Goldmund turntable, so I know what I’m talking about). The Koetsu organizes the sound and puts everything in the middle where it belongs, but with a wide and deep soundstage. (“Honey” is the term my Aussie buds use to describe the K. sound - I’m in love with my own Koetsu Black as well - B.) I constructed a new counterweight which is solid aluminumand steel by measuring the original weights and trying to get as close as possible. Of course the first attempt ended up way too heavy, so I had to machine the sides a little more until it worked. Adjusting the tracking force is a little difficult now - if you move the weight a little too far you’re immediately off 1015 grams! I didn’t change anything on the tonearm, so I could always go back to the factory setup But it was worth the trouble. The sound is very airy now. Remember the tracking force is still 2.0 grams, but the damping, other than the friction in the bearings, is gone. I like it better the way it is now, but some reader will disagree and use a spoon wading through a basin of silicone oil! Anyway, my Benz MC-2 worked great for a year or so but then the sound slowly began to degrade. At first I thought I had some bad records, but I began to notice how the strong bass and clear highs were dissappearing, and the soundstage width and depth began to dissappear. After some troubleshooting we tracked the problem down to the cartridge. It became so bad that I had to send the cartridge back to the factory. It turned out to be a suspension related problem. What happened was the little ”rubber” suspension ring had dried out and become hard so that it limited the cantilever free travel. I later heard that this happened to other cartridges too. The factory replaced the “rubber”ring with one of some other material and all work fine now. For me this cartridge is a typical MC cartridge - deepbass, laid back midrange and good highs with a lot of detail. I used 2.1 grams tracking force and 24 degrees VTA (rear of cartridge/tonearm slightly down). the factory recommends a tracking force of 1.8 grams, but I didn’t like it so much, it was somewhat thin sounding. The channel separation is given as 28dB and it puts out 0.3 mV which means that an excellent phono stage is a must. the little weights off the tonearm? The idea was that by constructing a new weight I could lower the center of the counterweight compared to the turnaxis (center of gravity) and move the weight closer to the vertical axis. This would give a more stable tonearm with respect to up and down movement (faster standstill) so it would play slightly warped records more easily. See drawing three for inspiration. Shortly after I completed the experiment with the counterweight I spotted an article about a Roksan tonearm upgrade called the Tabriz Tonearm with 2i counterweight. On the Roksan Artemiz counterweight this idea has been taken to the limit, the weight rests only on a spike so it can swing freely without moving forward or backward and altering the tracking force. This works great and I’m a little surprised not to see more manufacturers picking up the idea. It’s probably a matter of taste. Right now I use all the above mods with great satisfaction. I use the Welborne Labs Phono1 kit in connection with a German made pre-preamp. I have about 63 dB gain (Phono-1, 36dB, pre-pre, 27 dB) which is a lot, but then again quite a lot of cartridges put out something in the neighborhood of 0.3 mV, so this is about what is needed. load. With a combination of a built-in spring and several weights this is a relatively easy adjustment to achieve on a Grado tonearm. Once the tonarm is set up it is a great tracker, but some recent developments made me curious. Some friends in the German audio community believe that a tonearm should have no damping at all, but rather should move as freely as possible in order to get that last little bit of air. One friend uses a Grado tonearm in which he took the damping completely out no spring load, just the counterweight load, and he reports good results. The Grado tonearm has one big counterweight and two small ones, so called micro-weights, for setting the gravity to spring force ratio. This brought up an idea what if I take out the spring load, construct one weight which is lower, actually below the cartridge, and take The loading is 47kohms. I tried 100K, 30K, 10K, and even no loading in the past, but I go back to 47Kohms every time. The capacitive loading is 100 pF. My system consists of a switching unit with stepped attenuator, two Welborne Laurel monoblocks with Cetron 300Bs and a full range Edgarhorn system (see October 97 VALVE). I found it unecesssary to use a preamp because all components put out more than 2 volts, enough to drive the laurels/Edgarhorns to disco level. However, I installed a buffer to compensate for the 20 ft. Kimber interconnects. Maybe Ron Welborne was right when he mentioned in his catalog “This is the last phono amp you will ever need”. Maybe that and a pair of triode amps and good horns is all we really need. MagneQuest Electronic Tonalities & making the world a better place for DIY Parallel Feed Output Transformers EXO-36 2.5K:8 ohms, 3 watts max, permalloy core, solid brass channel frame. 2A3, 6A3, 6B4 - $270 pr. Airgapped Single Ended Output Transformers TFA-204 3K:16,8,4 ohms, 8 watts, 60 mA - $198 pr. DS-025 2.5K:16,8,4 ohms, 20 watts, 60 mA - $298 pr. EXO-35 2.5K:16 ohms version of above - $270 pr. DS- 050 5K:16,8,4, ohms, 20 watts, 40 mA - $350 pr. EXO-45 5K:8 ohms, 2 watts max, permalloy core, solid brass channel frame. 45, 71A, 417A/5842, 6CK4, 6DN7 - $270 pr. EXO-46 5K:16 ohms version of above - $270 pr. TFA-2004 3K:16,8,4 ohms, 15 watts max, black end bells, M4 core, 300B, VV32, VV52 - $350 pr. TFA-2004 Pinstripe ( M6 with Permalloy “pinstripes”), polished solid brass brass bell ends, 300B , VV32, VV52 - $500 pr. M Q RS-330 3K:16,8,4, ohms, 30 watts, 80 mA, - $500 pr. RS-500 5K:16,8,4 ohms, 40 watts, 80 mA, - $600 pr. RS-520 2.5K:16,8,4 ohms, 50 watts, 120 mA - $700 pr. FS-100 10K:16, 8, 4 ohms, 40 watts, 80mA - regular $850 pr. - SPECIAL SALE, $450 pair! Push Pull Output Transformers TFA-2004 all Permalloy core, 12 watts max, polished solid brass bell ends, 300B, VV32 - $600 pr. NEW - EXO-50 5K:16,8,4 ohms, 20 watts max, M6 with Permalloy “pinstripes”, solid brass bell ends, 300B, 845, SV811A - $550 pr. Parallel Feed Linestage Transformers B7 15K:500 ohmsCT, parallel feed line stage transformer, permalloy core, brass channel frame, 56,76,6J5, 6SN7,5965,5670, 12AV7 - $198 pr. B7 5K: 500 ohmsCT, as above, 417A./5842, 437A/3A-167M, 5687 - $198 pr. MQ-420-CL 6600CT:16,8 ohms 30 watts - regular $298 pr. - SPECIAL, $238 pair! MQ-431 4300CT: 16,8 ohms 60 watts - regular $378 pr. - SPECIAL, $298 pair! MQ-451-CL 2200CT:16,8,4, ohms, 120 watts - regular $458 pr. - SPECIAL, $398 pair! MQ-470-CL 4300CT:16,8,4 ohms, 35 watts - regular $298 pr. - SPECIAL $238 pair! Peerless 20-20 series model S-271-A, configure as 5000CT:16,8,4,1 ohms, 200 mA, 80 watts or 1250CT:16,8,4,1, ohms, 400 mA, 80 watts - $1200 pr. Parallel Feed Interstage Transformer RIT-5 5K:5K (1:1), M6, channel frame - $250 pr. RIT-5 as above, but with bell ends - $300 pr. add $100 per pair for Permalloy core Parallel Feed Plate Loading Chokes Peerless 20-20 series S-275-A, configure as 4000CT: 16,8,4,2 or 8000: 32,.16,8,4 or 12,000:48,24,12,6 ohms, 120 mA, 80 watts - $1200 pr. Power Transformers PGP 8.1 120V primary, secondaries 350-0-350 75 mA, 6.3V 2A, 2X 2.5V 1.25A, horizontal (drop through) mount, solder terminals - $165 pr. BCP-16 1mA, 425H, 4400oms DCR , channel frame - $80 pr. BCP-14 10mA, 100H, 2075 ohms DCR, channel frame, - $90 pr. EXO-01 20 mA, 100H, 985 ohms DCR, brass channel frame $110 pr. 5504 universal primary, secondaries 350-0-350 100 mA, 5V 3A, 6.3V .5A, 2X 2.5V 1.25A, black bell ends - $350 pr. Filter Chokes BCM-19 10H, 200 mA, 109 ohms DCR - $150 pr. NEW EXO-99 dual bobbin, configure for10 mA 600H or 20mA 150H, 1129 ohms DCR, brass channel frame - $198 pr. NEW B.F.F.C. 10H, 200 mA, 18 ohms DCR!!!!!!!! - $298 pr. BCP-15 50mA, 40H, 550 ohms DCR, channel frame - $90 pr. EXO-03 60 mA, 30H, 344 ohms DCR, brass channel frame - $130 pr. EXO-04 60 mA, 50H, 317 ohms DCR, black bell ends - $198 pr. B.A.C. 80 mA, 50H, black bell ends, - $298 pr. Electronic Tonalities 360-697-1936 www.bottlehead.com VALVE the magazine of astounding sound Groove Thang Docs phono preamp O-Glow, converting the Baby Ongaku to Active Loaded Direct Coupled operation Brainiac on the British ultrafi scene and more Heavy Metal direct coupled differential PP EL84 amp why cant Johnny read schematics? more VSAC 98 photos in color! volume 6 number 2 1999 B-Glow the latest buzz - a single ended 300B amp kit from Electronic Tonalities active loaded 5965 driver MagneQuest TFA-204 air gapped output transformer 8 watts of sonic honey $900 the pair, you just supply the 300 bees, er, 300Bs VALVE the magazine of astounding sound Editor and Publisher Dan Dr. Bottlehead Schmalle Chief Administrator Queen Eileen Schmalle Resident Smart Guy and Technical Editor Paul Braniac Joppa Graphic Design Bruce Badd Dawg Borley Resident Hot Iron and Dr. Bs Bodyguard John Smoothplate Tucker Big gun OEM advisor Michael Airgap LaFevre The Guy With Answers John Buddha Camille Contributing Editors David Full Track Dintenfass Crazy Eric Lenius Our mailing address: VALVE P.O. Box 2786 Poulsbo, WA 98370 by phone: 360-697-1936 business hours: 9-5 PST, Mon -Fri fax: 360-697-3348 e-mail - [email protected] website - http://www.bottlehead.com VALVE in no way assumes responsibility for anyone harming themselves through exposure to the contents of this magazine. We believe electrons flow from minus to plus, and that they can kill you along the way if youre not careful. Vacuum tube audio equipment operates at potentially lethal voltages. Always treat it with respect. Many ideas published in this magazine are untried, and involve the use of potentially dangerous parts and tools. In attempting any idea or project published herein, you assume total responsibility for your actions and any harm caused to yourself or others. Please, be careful! This publication is produced as a service to the audio community and is wholly owned and published by Electronic Tonalities. The intent of this publication is to offer ideas to inspire and educate audiophiles in an effort to increase their understanding of the audio equipment they use and cherish. Blatant copying of the circuits published in this magazine for use in commercial products shows a complete lack of original thought. editors thing Did we do the right thing? We expected some bruhaha about our changing over from hardcopy to what seems to have affectionately been dubbed CYBERVALVE by our readers, but in fact, the positive response has been almost overwhelming. Naturally we had a few folks come to us with technical problems, but we seemed to have sorted most of them out as being due to the use of outdated versions of Acrobat Reader. The folks who didnt have computers were urged to check out CYBERVALVE at the local library or cybercafe, and those who did seemed pleasantly surprised. A few folks complained about the download time. Ever hear the saying anything worth having is worth waiting for? I dont plan on cutting the quality of this publication just to improve the download time, so thats just the way it is. A 20 minute download is a lot shorter than three days in the mail, homes. The bottom line is this VALVE in hardcopy peaked at a total of 650 subscribers. The first issue of CYBERVALVE, a bigger, better issue than ever before, was accessed over 7500 times in four weeks, from an average of 1063 unique addresses per week. Did we do the right thing? Can you say no brainer? and another thing We welcome new advertisers to this new version of VALVE. Dont let the fact that this mag is coming from bottlehead.com keep you from talking to us about advertising a competitive product. United we stand and all that, we want to see everyone do well in this biz. You may note that one of our biggest competitors (and a very good friend at that) advertises in VALVE. If youd like to advertise in a magazine that gets 7500 accesses a month, by folks who are looking for kits, parts, and any tube audio related stuff, get in touch with us. We offer rates that are much lower than the hardcopy mags - $100 per issue for a full page (7.5x10) color ad, and can deliver a new ad to the public in a much shorter time frame than the printed media. You can send us the ad in Pagemaker, Publisher or Acrobat format, or send us your photos and copy and we can put the ad together for you and get it into the next issue for an additional $40. Our goal is to get a new issue out every six weeks, so advertise early and advertise often! Dont let the blue smoke out, Doc B. on the cover This is the prototype of our new B-Glow 300B SE amp kit.The conventional airgapped, RC coupled, fixed bias circuit has really turned out to be a pleasant surprise - great bottom end, absolutely killer midrange, sweet clear highs. The prototype was finished with gloss black powder coat on the chassis plate, a clear polymer coating on the poplar base, and metallic faux granite on the i nductor s. Brass hardware replaced the stock plated steel. The wire is a combination of Jena Labs 18 ga. hookup and our new house brand 20.5 ga. solid wire. Groove Thang a phono stage by Doc B. If your CD sounds better than your vinyl, theres something seriously wrong with your vinyl setup, B. Geez, was I getting tired of hearing that one. a little history Ive been futzing around with a few different pieces of phono gear over the years, but never really reaching anything like satisfaction with the setups Id use. Been through the TD-124/SME3009/ Denon DL-103 route, actually that was my second 124 (hell, man, I had a TD-124 when I was 18, with a big clunky Rek O Kut arm and an original ADC-1 cartridge, what took the rest of you so long to figure out theyre a good Ttable?) For now Ive settled on a big ol Denon DP6000 I got as a commission on a fairly hefty antique radio sale I did a few years ago. It has a Denon DA-305 tonarm on it, nothing to write home about, save for the fact that it is fairly massy. The table also has a second arm mounting board, which has been through a Grace 747 and now sports a Linn Basik thats been sleeved with heatshrink and the counterweight has been replaced with one of Andy Barthas littlest Whatchamacallits with a hole poked in it to add a little mass and damping. The search for a decent tonearm continues, and theres a certain long skinny piece of ebony that sits in my woodpile that subliminally beckons me to try to DIY one whenever I walk by. The concern for mass stems from the fact that I love low output moving coil cartridges, and them moving coils want to hang off a beefy stick. They also want some step up, and for this I have used a Denon step up transformer, for lack of anything else. I did have a Levison JC-1 for a while, but somehow talked myself into the whole gotta have transformers bit at one point and sold it. To its credit the trans is very versatile, it has switched inputs for two cartridges and 40 ohm and 3 ohm taps. But unfortunately Ive heard Koetsu and Sun MC step trannies, so Im well aware that this aint the best there is, although a replacement of the stock output cable with our new trick wire helped open things up a wee bit. Mikey keeps talking about these incredible step up trannies he wants to wind someday, but he knows Im too much of a rag picker to be able to afford all that fancy ass triple mu metal shielding, so we wont hear a MagneQuest MC stepup until someone with deeper pockets than Doc B. steps up to the plate and custom orders a few sets. OK, I skipped over the cartridge, I know that. Been through my fair share, over the years, from that ADC-1, through Sonus Blues, cheapo Empires and ATs, Grados of various persuasions, cheapo to middling good Shures, an Audioquest AQ-404 that I bought in a fit of self pity when my first wife dumped me, a DL-103 I scored for $50 right before everyone started saying how great they were, etc., etc. No doubt in my mind that the low output MCs always worked best for me. I note that in the 50s MC cartridges were called dynamic cartridges. Ill drink to that. So now I have a Koestu Black I picked up used from Victor Meurisse, and a Fidelity Research FR-1 that my bud Stan Webb found at Goodwill, in the box, with the papers, for something like 50 cents. The man has an eye for the good deal, and I felt like I got a great deal even when I offered him a 10000% profit for it So now I have two carts with piddling output, about 0.3mV, and distinctly different characters. The K is like honey on top, so sweet you think it might be rolled off, until you hear a cymbal. Its clean and clear, but laid back. Bass? Holy shit! Put on some 70s fonk with that really heavy analog synth, and tear the roof off the mutha sucka. The K is quite happy at 40 ohms, I found it quicker but a bit dry into 47K. The FR-1 is the other end of the spectrum, more like what weve come to accept as the MC sound, I guess. Very clean and beautifully open, very present, to the point of accentuating surface noise a bit too much. Maybe not so hot on the bottom, demanding 3 ohms to sound with any weight at all. Fooling with the VTA helps this somewhat, but my hunch is that this is in part due to the Basik its mounted on, and I hope at some point to try the FR-64 tonearm the cart was designed to mount in, which I understand is the Hulk Hogan of tonearms, with a bigass armtube and a 2 lb. weight hanging from its base, under the turntable plinth. a starting point So enough with the preamble, you thought this article was gonna give you a cookbook phono preamp and Doc is just reminiscing, right? Well, this aint that. I was fortunate enough to have been given one of George Wrights first phono stage prototypes (OK, I admit it, George has been so kind as to send me three preamps over the years, two of which have wandered off to other guys systems, never to be heard from again). How good are they? Suffice it to say that its the one I recommend when anyone calls asking, and everyone who buys one loves it. But hey, Im Doc B., no matter how good this thing is I just gotta build my own and convince myself its better, ya know? George based his design on the now classic RCA phono stage, a two stage preamp with passive RIAA eq, which can be found in the RC-30 tube manual. He modified the design extensively, incorporating very high gain 6ER5 tubes. He designed his preamp to work with MM cartridges, and to drive any kind of preamp you might want to plug it into, including a cathode follower output for the purpose. Check out May 95 VALVE for the scoop. I wanted to do a couple of thing differently, so I kinda cobbled up one of the early protos George had given me. The earliest experiment was to upgrade coupling caps and wire, the usual know nothing type of upgrades. Nice subtle changes, but this was not what I was about, so the first thing to happen was the cathode resistors on the 6ER5s went in the dumper and I shoe- horned in four Ni-Cd AA batteries instead, into a box even smaller than the production preamp come in. George's preamp is setup for MM cartridges, like I said, and George has worked hard to get a very extended top end (some say a bit bright). This is a superb complement to Grados and Shures, but some of the MCs I was using got pretty lean sounding through the preamp. The AAs did a nice job of kicking up the bass, not necessarily with a great deal of control, but with ample quantity. I should point out that in the process of adding the batteries, the operating points remained the same, with the 6ER5 grids biased to -1.2V giving a low, like around 1 mA current draw. This low current operation keeps the 6ER5s, with their rather high gain, very quiet. One thing I wanted to mess with was trying a higher current draw to see if I could richen the sound up a bit without adding too much noise. I planned on running this preamp into a Soul Sister line stage with 100K input impedance, through a short cable, so I didn't feel the need for the cathode follower output stage George designs into his preamp. Output now comes directly off the coupling cap that follows the second 6ER5 stage. And of course I had to try to build the preamp with C4S loads. These could turn out to be the perfect load for a phono preamp gain stage, they give two advantages we seek - high gain (the full mu of the tube) and low noise, doing a superb job of isolating power supply noise, and replacing the typical noisy plate load resistor. Since I wanted to hear the 6ER5s with higher current running through them, I set the C4S atop each 6ER5 to run at 10 mA and went back to resistors on the cathodes. A word to the wise here, this preamp is still in the cut and try stages. Fiddle with the cathode bias resistor to get the plate voltages you want. So the basic two stage with passive RIAA circuit came out as shown below. I had been very pleasantly surprised at the effect of using gaseous shunt regulators with the Soul Sister line stage (really opens up the top end), so I employed the same ideas with the phono preamp, using the original Wright prototype series regulated power supply chassis as the starting point The series reg and tube rectifier came out and the VR tubes went into the existing holes. It would be much better to put the shunt regulator as close to the C4S boards as possible, and I will probably move these tubes to the holes where the cathode followers lived on the phono preamp chassis in the future. Ultrafast recovery soft start diodes replaced the existing rectifiers in the high voltage supply and heater supplies, and I reworked the existing caps and resistors into a CLCR filter ahead of the shunt regulator. Groove Thang Phono Stage - one channel 300VDC B+ R1 100 ohms 100 ohm C4S active loads 2N2907A 2N2907A MJE 350 R2 150K 1/2W MJE 350 190VDC 150K ohms 190VDC 6ER5 6ER5 .47 mfd 400V 402K 1/4W in 0.1 mfd 400V 47K 1/4W the adventurous will want to play with this cartridge loading resistor 536K 1/4W 1.2VDC 120 ohms 20K 1/4W 0.012 mfd .003 mfd passive RIAA EQ 1.2 VDC 120 ohms out to line stage The whole PS is shown below: And now a confession. I was hoping to get low enough noise to be able to plug the cartridges directly into the input of this preamp, and get rid of the step up device. I installed a 47 ohm input resistor and cranked the volume pots on the Soul Sister waaay up. The sound was marvelous, faster with more depth and detail, but just a little too noisy and a bit shy gainwise. Maybe some future improvements in layout will help, but right now the limiting factor to direct input from low output cartridges seems to be finding 6ER5s with a low enough noise level. I suspect it woud be interesting to try this preamp with nuvistors, too. I don’t have a clue whether they would be any better,(they have a rep for lots of microphony, so maybe not, but it would be fun to try. So back went a 47K resistor across the input, and in went the step up trans. Hmmm, not bad! The new circuit seems to have alleviated some of the vagaries I felt the step up trans was producing. medium Whatchamacallits. A few small Whatchamacallits went around the armboard. All of this extra mass seems to tighten things up and offer a bit better isolation. So you need a description of the sonics now, huh. Well, I finally like my vinyl set up better than my CD. It's a little fatter than the CD setup, but the dynamics are like, there, yowsa!! But the biggest improvement was when I pulled off the old rubber mat and put six evenly spaced small Whatchamacallits on the aluminum platter. The records now "float" on these pucks. I had to add a piece of 1/4" aluminum tubing to extend the spindle to keep the center hole of the record from slipping around and creating wow, and of course I had to raise the tonearm height. Once this was done the improvement was, as we say, not subtle! The reduction of background noise was quite significant. Bass is really something with the Koetsu, it gets way down there, and with good control. Living Stereos that seemed too soft and lush now have impact and better, if not perfect, presence. Vocals are tighter with less euphony. Mo' natchul. I should mention my other recent tweaks. Along with using our new long crystal copper cables I covered the Denon plinth with big Whatchamacallits (well, one in each corner really) and set the base on three Give Andy Bartha a call at 954-583-7866 ET and get some of these ugly little pucks, they are really fun to play with.! Groove Thang Q&D power supply (derived from Wright phono preamp supply) adjust this resistor to drop raw B+ to 300V at the VR tubes. Use a curent draw of 70 mA to calculate R=V/I and VxIx2 to calculate wattage UF4007 fast recovery diodes 1A 600VCT or higher 70 mA 120VAC 300V to C4S loads 8H 47 mfd Schottky diodes 12.6V 1A 470 mfd 0D3 0D3 0.33 ohms 1W 2x22000 12VDC to mfd series wired heaters For best performance put the power supply in a chassis separate from the phono preamp. The VR tubes should be on the preamp chassis very near the C4S boards for best regulation New exotica from First Impression Music FIM CD019 Favorite Chinese Instrumentals The Jin Ying Soloists 1 Like Wave Again The Sand (Pipa solo with ensemble) 4:36 2 Singing the Night among Fishing Boats (Jung solo) 4:15 3 Night (Percussion ensemble) 5:54 4 Love Song Of The Grassland (Tung-hsiao with ensemble) 2:34 5 Ducks Quacking (Percussion ensemble) 4:00 6 Love At The Fair (Er-hu solo with ensemble) 5:04 7 The Fishing Song (Bawoo solo with ensemble) 4:53 8 Happy Reunion (Xylophone solo with ensemble) 2:55 9 Chinese Martial Art (Emsemble) 1:43 10 The Flowing Stream (Er-hu solo with Yang chin) 8:25 11 Spenpadei Folksong (Yang-chin solo with ensemble) 4:32 12 Autumn Moon (Er-hu solo with ensemble) 7:06 13 Moonlight Over The Spring River (ensemble) 9:22 14 Variation On Yang City Tune (Ku-jung solo) 5:36 FIM CD020 A Vocal Tribute to Ben Webster Jacintha, Vocal Teddy Edwards, tenor sax; Kei Akagi, piano; Darek Oles, bass; Larance Marable, drums 1 Georgia On My Mind (Gorrell-Carmichael/BMI) 5:19 2 The Look Of Love (Baccharach-David/ASCAP) 4:08 3 Danny Boy (Traditional) 7:26 4 Somewhere Over The Rainbow (Harburg-Allen/ASCAP) 9:43 5 Startdust (Parish-Carmichael/ASCAP) 6:40 6 In The Wee Small Hours Of Morning (Hillard-Mann/ASCAP) 4:15 7 Tenderly (Lawrence-Gross/ ASCAP) 5:25 8 Our Love Is Here To Stay (George & Ira Gershwin/ ASCAP) 3:19 9 How Long Has This Been Going On? (George & Ira Gershwin/ASCAP) 5:28 10 Pennies From Heaven (Burke-Johnston/ ASCAP) 3:12 #189 16149 Redmond Way Redmond, WA 98052 http://www.fimpression.com Tel: 425-868-5326 Fax: 425-836-9061 you asked for it O-Glow a conversion of the Baby Ongaku into a big brother version of Afterglow By Doc B. Weve received several calls lately from folks whove built Gordon Rankins great Baby Ongaku design, so named in an article by Frank Reps in Issue 9 of Sound Practices. The design was originally drawn up by Gordon for Mike Lafevre to use as a giveaway application for MagneQuest customers who purchased DS-025 output transformers and 5504 power transformers. A lot of folks have called us asking if it would be feasible to convert the circuitry of the Baby-O, as it is affectionately called, to roughly the same direct coupled, active loaded topology as the Afterglow. Sure. The basic parts are there, and the quality of the iron should yield up a sort of superglow. NOTE that I dont have a Baby-O on hand as I write this, so it may take a bit of tweaking to get the voltages of this direct coupled conversion just the way you want them. Such are the trials of the hardcore direct coupler. To take the design as close as possible to the Afterglow in terms of sonics the 5V4 should be replaced with a pair of ultrafast recovery soft start rectifier diodes. This will lower the power supply impedance which can help dynamics. It will also help to get the voltages up where we want them to be, as the voltage drop across the solid state rectifiers is less than the tube rectifier. The .68 mfd cap at the input of the power supply filter must be increased, maybe to 40-100 mfd to get the B+ up to what we will need for direct coupling of the circuit, a critical contributor of the Afterglow sound. With the power transformer secondary voltage of 720VCT we should get into the ballpark of voltage we get from the PGP 8.1 trans used in the Afterglow. In a pinch that 10 mfd cap connected to the 12AT7 SRPP could be used to replace the .68 cap if it has a high enough voltage rating, otherwise use a 600V or higher rated capacitor and go ahead and up the value to 100 mfd. While youre at the output of the PS filter, disconnect the 390K and 100K voltage divider resistors and the 22uf bypass cap that connect to the CT of the 6.3V filament winding, you wont need em for the new driver stage. The center tap can be left floating, or you can tie it to ground. Choose the way that is quietest. The plate of our 2A3 will be sitting at roughly 400-440 VDC, and we will want the 2A3 filament to float at about 145VDC. The 2A3 will run at 60 mA, so we will need bias of -45 volts between the filament and the grid. This puts our direct coupled 2A3 grid and 5965 plate both at 100VDC. To set the filament at 145VDC at 60 mA, we will need to change our 1Kohm 2A3 cathode resistor to 3000 ohms (yes this is the right value, youll see why when we explain the connection of our 5965 active load) and it will need to be a 10 watt wirewound resistor. may be paralleled to it to achieve the 50 mfd value, although you may be sacrificing a bit of bass performance compared to the stock Afterglow. We will use 1/2 of a 5965 for our active loaded driver, because a 12AT7 will become so sensitive with the C4S as to make the amps volume a bit hair trigger to adjust. Using 1/2 of the 5965 is kind of cool, if one triode wears out, we can always wire up the other half! The SRPP is replaced by a C4S active load on top of the 5965. In the process of removing the SRPP the 7.5K ohm dropping resistor, the 10 uF bypass cap, and the 333 ohm bias resistor associated with the top half of the SRPP are removed. We want to run our 5965 at 100V and 5 mA, so R1 on the C4S board should be about 190 ohms, to set our 5965's current draw to 5 mA. R2 needs to be about 73Kohms. See the C4S manual for details on setting this up. The cathode bias resistor of the 5965 needs to be about 280 ohms. No cathode bypass cap is needed. The input grid resistor of the 5965 can stay at 221Kohms. Obviously the 221K grid resistor on the 2A3 grid, and the .47 mfd coupling cap are removed for this direct coupled amp and the plate of the 5965 is coupled directly to the 2A3s grid. NOTE once again, beware that these voltages may be off a bit from what you actually get. The point here is to get 45V difference between the 2A3 filament and the grid. If the plate voltage is a little lower or higher, dont sweat it. If its a lot different (hey we dont have a Baby-O here to test), let us know and we can clarify the values needed. Another unusual feature borrowed from the Afterglow design is the connection of the C4S boards input, the R1 current set resistor to the top of the 2A3s cathode resistor. This seems an odd way to supply the driver tube, but in practice works extremely well, the most notable improvement being a reduction of the noise floor when compared with the more conventional approach of feeding the load thru a dropping resistor directly from the output of the power supply. This connection also explains why the 2A3s cathode resistor is 3000 ohms. Only 50 mA passes thru the cathode resistor, while another 7 mA passes thru the C4S, for a total of 57 mA total current draw through the 2A3. A 200 mfd capacitor rated for at least 200V should be used as the cathode bypass cap, replacing the 30 mfd cap specd in the original design. If the original 30 mfd cap is rated for 200V or better, the 20 mfd @ 250V cap removed with the voltage divider So there you have it, now you can try out another nice 2A3 circuit on that Baby-O you built. And if you are looking to build a super 2A3 amp on your own chassis, the design would certainly be a worthwhile contender for a scratchbuilt project. o-glow a little journey to the home of Kevin Scott By Paul Joppa When I was in England in 1997, I tried to visit Simon Shilton, the transformer maker. That didnt work out, but he recommended that I try to see Kevin Scott and hear his speakers. Id never heard of him, his company, Living Voice (#2 Carlyle Road, West Bridgeford, Nottingham NG2 7NQ United Kingdom), or the Air Partner and Air Scout speakers. But it seemed like a worthwhile thing to try, as long as we were going to Nottingham anyhow. We stayed at a nice pub that must have been built about the time trains were invented. It was close to the train station anyhow, and a short walk to the castle. There are several pubs near the castle, built into the old tunnels under the castle, that all claim to be the oldest pubs in England. Everything seemed easily accessible, and West Bridgeford was also pretty close - but Kevin suggested strongly that a cab would be the best way to find his place. He was right. I had a map, and was diligently following the cabs route - for about the first half mile! After that, it was hopelessly confusing for an outsider like me. Eventually however, we pulled up in front of his house on a pleasant residential street and I knocked on his door. I walked into his fairly small living room, and was stunned by these huge monoliths, in piano black and beautifully finished birds-eye maple. They stood nearly 4 ft high with a nearly 2 ft square footprint. Then I noticed the bass horn between them, maybe 30 in high but at least 5 ft wide and 2-3 feet deep. The speakers completely filled the narrow end of the room. OK, Im thinking, the satellites are 16 cubic feet each this guy must be pretty serious! He immediately put some music on, before I can say more than Hello, Im Paul... - a real believer in the VALVE philosophy, Shut Up and Listen! The sound is simply stunning - see the comments later. The system that we listened to included a Wadia 860 CD, Simon Shiltons lovely preamp (basic anode follower, choke-input power supply - see his web page for details), and an Art Audio amplifier with VV30B outputs driving Sowter output transformers for 13 watts. The bass he feels is far more important than you would think - any shortcomings here will muck up the midrange. Its surprising, he says, how often a change in the bass results in a percieved change at much higher frequencies. Its also the biggest challenge; its very difficult to obtain clean high-level bass. I must say, his system certainly supported this, showing the best combination of extension, resolution, and impact that Ive ever heard from a speaker system. In between the cuts, we talked about various issues. Kevin has lots of opinions, and wasnt shy about sharing them. Most seem to be based on his own experiences, and he often deplored the incestuous repeating of others opinions which characterizes much of the high end dialog today. Perhaps Id better describe the speakers we were listening to. These are his smaller systems; there is also a larger model without the subwoofer. All his systems are made as much as possible by other craftsmen; he noted it took a long time to find a good enough cabinet maker but it was worth the effort. Hes right, the cabinets are real works of art. The drivers are all from Vitavox, except the tweeter ( JBL), but most are modified in various ways to his specs. The systems are way out of my league at some $30,000 a pair plus another $12,500 for the woofer - I felt lucky to have been able to spend so much time listening to them. He runs the business as much from his home as from his (by-appointment-only) shop. He seems to spend his time listening to music and talking about music systems with other enthusiasts, with occasional breaks for beer and mountain biking. What a great life! On amplifiers, he thinks most single-ended amps have inadequate power supplies. Theres a guy named Gary Dews who makes amps and power supplies under the Border Patrol name (Simon Shilton also mentioned him) who has experimented extensively, and in fact sells upgrade power supplies for many SE amps. Kevin claims these power supplies make major improvements in sound, even on cheap amps. He also thinks theres no point in bothering with 211s, 845s, etc - they just never have the full-range resolution of the smaller audio tubes. In general, he has found that high-frequency extension is surprisingly important - hence for example interstage transformers are to be avoided unless you can afford a really good one. Kevin is very enthusiastic about component quality. I gathered he had spend considerable effort investigating components for every detail of these speakers. He likes Hovland capacitors, finding most others dull (and even the best electrolytics dark sounding). He uses big, air-core inductors - and at the 90Hz subwoofer crossover, they must be pretty darn big! Starting at the bottom, the sub has two 12" Vitavox woofers (a custom design for this speaker) in a classic folded horn like the original Shearer theater design. It covers 40-90Hz. I did not find out anything about the crossover, except that it was passive, everything running off the Art Audio amp. The woofer of the satellites is another 12" Vitavox, the same one as the subs Kevin feels this helps the integration. The suspension is quite stiff, and I assume the cone is quite light to obtain the claimed 105dB sensitivity. The surround is the tried-and-true doped folded paper; the cone itself is undoped paper. The magnet is quite large, and ceramic - he actually prefers the sound of these drivers with ceramic magnets to that with Alnico, after trying both. It is front-radiating and backloaded with a large horn, exiting with a mouth about 18" square at floor level. Visible internal curves are smooth. The horn is said to go down to 50 or 60 Hz in-room without the sub; with the sub it covers 90 to probably around 200, then direct radiation takes over up to the crossover at 500 Hz - much like a classic Lowther horn in the bass, but with dimensions twice as big, and a shorter horn due to the higher cutoff. The midrange crossover is basically a classic second-order type, with one trick that he was a little cagey about except to say it was quite cheap but makes a significant difference. For the most part, effort was spent on component selection rather than crossover topology elaboration. The midrange is a Vitavox horn and driver with a 2.75 in custom diaphragm - very similar to the classic large Altec units. The diaphragm surround is a polymer with radial corrugations. The horn is interesting - it looks a lot like a large Altec (its a full 2 ft wide, and I suppose 10" high), but the dividers go almost all the way back to the throat - and the side walls are curved in the half closest to the throat, so that its more exponential than radial in the first half of the horn. It becomes radial for better directivity control in the mouth half. Specified directivity is 120 by 90 degrees. Brainiacs Heavy Metal ...an occasional review of some nifty chunk of iron (usually cheap!) by Paul Joppa Todays Topic: the Champ output transformer The dividers ring a bit when tapped, but the horn walls are very well damped. The mids run to 10 kHz with a natural rolloff; the last octave is handled by a JBL slot tweeter which he prefers by a wide margin over the much-touted Audax. Unusally, its rotated so the slot is 45 degrees from the vertical. This is not a review, just some impressions based on a few hours listening in Kevins room, to his music in his system - but this puppy sounds darn good. The system was being played at levels considerably higher than I would use myself, and I was impressed with the effortless ease with which these levels were handled. I have never heard bass before with such convincing solidity. Not even the big Wilsons can do what a really good bass horn can do. The sound was wonderfully well integrated. I have admired John Tuckers Exemplars in this respect ever since I first heard them, as being far and away better than any other horn system Ive heard - but this was if anything better. And the treble nasties, which I hear in every horn system Ive ever run across to some extent, seem to be entirely missing. (The treble itself was certainly not missing - cymbals for example were especially crisp and lifelike). I spent some 3 hours with Kevin, probably 2/3 of it listening to this system at levels I would not normally tolerate, and I was still not tired of it at the end. I dont know what it is, but theres some real magic here. Only twice did I hear any hint of coloration (and we went through a wide variety of music) - a bit of shout on male voice, and some low violin once. I suspect these were horn resonances, but in any case they are rare exceptions to the generally uncolored sound. There was no chestiness, no boom, no tizz, no high-level treble crunch (even with massed strings at 10 dB above concert-hall levels). Percussive transients were especially well-handled. Unusually in my experience, these systems were very listenable fairly close in - even 5 ft from the speakers the sound was still well integrated, and backing up as far as I could, some 15-20 feet away made it worse rather than better. The Champ amp is a small (5-watt) guitar amplifier, usually with a 6V6 output tube and an 8-inch speaker of 4 or 8 ohms. This transformer is sold as a replacement for burned-out units in these amps. I got mne from Angela Instruments for $25; they claim it is a little heavier duty than the usual replacement unit. It weighs 15 oz on my kitchen scale; the lamination stack is 2.25" tall x 1.875: wide x 0.75" thick. It appears to be air-gapped, secondary outside, primary inside. On my test bench I measured the following values: slope. With tweeters that have an inductive impedance rise, the treble should be even better. Turns ratio: 26.5 Primary:235 ohm DC Secondary: 0.36 ohm Leakage ca. 0.07 H Capacitance: ca 34 pF DC current: Inductance with 12v/ 60Hz excitation is 10.5H at 10 mA, falling to 5.25H at 90 mA. I would rate it at 45 mA, where inductance is 8.7H. With a 4 ohm load, impedance is 3300 ohms and losses are 0.7dB. It should give 3.3 watts at 60 Hz. . Small signal frequency response with a 1.5 to 2k plate resistance is within 3dB from 21 Hz to 10 kHz. This unit is unusual in that there is one lamination on each side that is interleaved, giving an unrealistic 15H at zero current. The capacitance is surprisingly small, so that high-frequencies are limited only by the leakage inductance giving a gentle The primary impedance with an 8 ohm load is 6100 ohms, and losses are small at 0.4 dB. Figuring power bandwidth as the frequency where the inductive impedance equals the load resistance, I rate this unit for 6 watts at 110 Hz. Small signal frequency response with a 1.5 to 2k plate resistance is within 3dB from 25 Hz to 17 kHz. Overall, while this is not the greatest transformer available, it is good enough to hear the music. Ive used it in my original spud amplifier with 417A/5842s; its also suitable for many TV vertical output triodes like the 6DN7, 6CK4, or 6EM7. A 45 would be perfect, though at todays prices they are beyond the budget area this transformer represents. And of course it was designed for 6V6 or 6BQ5 service. Out wit h t he Old We are closing out the KR Enterprise VV Valves to make room for the new generation of KR tubes. All sale tubes below have the KR 1 year warranty from date of purchase. Visit our website for KR pictures, specs and curves. http://www.welbornelabs.com/krhome.htm Please Note: These VV Valves all have 2A filament current requirements. Please check your equipment specification before ordering and make sure they will operate in your amps. No returns on these sale items. VV300B...the following are all electrically the same tube, just different glass shapes and color. The cylinder tubes are just that...they have a cylindrical shape with a flat top. VV300B regular transparent glass $200 per pair VV300BL regular blue glass $200 per pair VV302BL regular blue glass $200 per pair VV302BC blue cylinder $200 per pair VV32B...these VV32Bs are all electrically the same tube except for glass color and shape. VV32B VV32BL VV32BC regular transparent glass all sold regular blue glass $250 per pair blue cylinder $250 per pair VV52B...these VV52Bs are all electrically the same tube except for glass color. VV52B VV52BL regular transparent glass $250 per pair Hurry, almost gone blue glass $250 per pair Hurry, almost gone Hurry, quantities are limited. All sales are final. Buy 2 pair... take a 5% discount. Buy 3 pair... take a 10% discount. In with the New New From KR Enterprise. All tubes feature a 2 year warranty. KR10 Dual Triode Pre-amp and Driver Tube. A 6SN7 on Steroids? $395.00/pair KR2A3 Single-Plate Vacuum Tube A great new single plate 2A3. 2.5V/2.5A filaments. 2-6 watts of glorious sound. $395.00/ pair KR PX25 Vacuum Tube A replica from the past. 4.0V/2.0A filaments. 8 watts. $435.00/pair KR300B Vacuum Tube An awesome 300B replacement. 7 to 14 watts, 5.0V/1.2A filaments. $435.00/pair KR300BXLS Vacuum Tube 8 to 20 watts of power and dynamics. 5.0V/1.2A filaments. $575.00 per pair Welborne Labs ph: 303.470.6585 fax: 303.791.5783 http://www.welbornelabs.com e-mail: [email protected] direct coupled differential driven El 84 amp by Feeling burnt out on single ended amps? Try this on for size - how about direct coupled differential driven EL 84 amp. That does not cost a million dollars to make. The amp featured in this article is one that I built for Mike Lafevre, using a design that Mr. Komoro developed. I was given permission to build this amp with his schematic, also to write a future article. I would not recommend this amp to beginners as it is not an easy amp to construct. Most single ended amps are a lot easier to construct than this amplifier. How would I rate the difficulty? Intermediate, at least a couple of amps under your belt or a couple of belts under your amp? For resonace dampening of course! To DHT or to not DHT that is the question? This amp was designed not to compete with the harmonically rich DHT PP amps that are more expensive to build. These amps are built to a price point. The greatest cost incurred is the cost of the Dynaco SCA 35. Down and out need an audio fix, cannot find one of these amps to strip? Mikey to the rescue, Magnequest is reproducing the Dynaco Z 565 transformer that is used in both the SCA 35 and ST35 amplifiers. The transformers are of better quality or equal, of course people will whine that they are not original. But they will not whine when they sound better. this EL 84 amp is like Sauvignon Blanc, slightly sweet with a clean finish. I said sound, you clown. Sorry, writing an article will drive you to drink. The amp has a very powerful, sweet and transparent sound - can you say holographic? I knew you could. As for the power tranny good luck, Hammonds suck. Be sure to dig deep if you go to Leeds Electronics, they might have a surplus transformer that will work. Electroprint will build custom power trannies to order. Wheres the beef? Solid state rectification, its true. I swear. Ask Herb, he will tell you. How about the ultimate version? Tube rectified, carbon resisters, monblocks, separate cathode bias resistor and Blackgate caps - these things are as smooth silk. Do not forget, too smooth, too boring! Its a tonal balancing act, every part is a natural tone control. Every part has a different resonance. The trick is to get every thing to resonate in natural harmony how will you know its right? You will feel it in your heart. How does it sound? One could say that Lets talk techno, geek! The cathodes of the 6DJ8 are feed a negative voltage, the voltage and current are set by the cathode resistor. Why ? This enables the tubes to operate with equal bias on each section. Here lies the kicker, this amp is direct coupled any changes in the driver tube will effect the output tube, so the filaments of the 6DJ8s are regulated. This ensures that the thermal emission of the heaters, are kept constant. I used a Velleman kit regulator board that is cheap enough to offset the cost of my labor that would be required to hard wire one. Powering the regulator I used a Radio Shack 12 volt transformer. Regulating the B+ would have taken up more real-estate then I had available. Also the sound that B+ regulation inflicts upon the signal is not my sound. A balance pot is used for each input tube to adjust the balance between each section. In order to monitor the balance of sections of the input tubes I connected a battery powered LCD meter. I would then adjust the pot until 0.00 was displayed on the meter. A drift up to 1.00 is acceptable, this much imbalance will not harm the tubes. The output tubes are biased with a cathode resistor on each channel. These resistors are mounted on the chassis for better thermal transfer. This amp is one of my favorite amps that I have built. We shall see how it fairs against the highly touted Acro 20/20 that I am restoring. The EL 84 tube is one that should be taken seriously. da basics Schematics look like Greek to you? by Doc B. A lot of new folks have been joining our ranks lately, which is awesome. While a few come from an electronics background, the majority of new bottleheads are die hard audio nuts who know what they like, but havent had the opportunity to get up to speed on the design end of the DIY game. While we go to great pains to make our kits buildable without any working knowledge of circuitry, anyone who is serious about this stuff and wants to continue to improve their system will eventually need to know how to read a schematic drawing of a circuit. To this end I will start to present here some basic symbols seen in typical tube audio circuits. Please dont bust my chops if you think I forgot something, there will be more of this in the future, and count on the fact that well cover what each component symbolized here really does in a circuit over the next few months. Here we go: Resistor - The squiggle implies that the electrons flowing through the resistor are forced to burn off a little energy as they fight their way through. Potentiometer - Now our squiggly line has an arrow pointing to it. The arrow represents the wiper that runs over the resistive track in the pot when you crank it up to scare the neighbors. Can also indicate any other form of adjustable resistor Capacitor - The two perpendicular lines with the gap between them represent the two charged surfaces (usually foil or a metallized coating) in the capacitor. The insulator, polypropylene, oil or whatever, would be in the gap. You will see here that one of the two perpendicular lines is curved. Sometimes both lines are straight. This curved line sits to the side with the lowest potential of a DC rated capacitor, the minus terminal. Inductor- The curly line represents the inductor coil and the straight lines represent the core material. One curly line makes a choke, two curly lines, one on each side of the straight lines, makes a t r a n s f o r m e r. Taps are signified by straight lines attached to the curly lines. Ground - a ground connection is represented in a lot of different ways, but the most common is either the three lines shown here or a triangle pointing down (to the ground, get it?) heated rectifier A directly heated tube is a tube in which the electrons boil directly off the filament. The V can also be called the heater in an indirectly heated tube. An indirectly heated tube has an additional element called the cathode which is heated by the heater to the point where it boils off electrons. The indirectly heated cathode is the sort of upside down L shaped thingy right above the heater (the filament in a DHT is often called the cathode too). Triode - Like the vacuum diode, the circle defines the entire tube, so a dual triode is often diagrammed with only half the circle enclosing the internals. The new element added to our basic vacuum diode is dashed line in the middle which represents the grid. Tetrode - This is like the triode, but now there is an additional dotted line above the grid. This is the screen. Diode (Solid State) The triangular arrowhead dealy bob represents the direction of current flow through the rectifier, and the line represents the cathode end, through which current is kept from flowing back in the reverse direction. Light Emitting Diode ( LED) - These are similar to the solid state diode, with the addition of little arrows to represent the light emission. Diode (Vacuum) Heres a little more c o m p l e x heiroglyphic. The circle defines the entire tube. The upside down T at the top is the plate of the diode. If there is one of these in a tube designated as a rectifier (which turns AC power into DC power) it is a half wave rectifier. If there are two of these in the circle, the tube is a full wave rectifier. The upside down V at the bottom is called the filament in a directly Pentode - This is like the tetrode but yet another dotted line is added, which represents the suppresor. cold cathode. Voltage Regulator Tube - the gaseous shunt regulator tube is designated with the familar upside down T for the plate, and a circle for the Switch - gotta turn the thing off (unless you just unplug stuff like Doc ). The angled line represents the moving switch contact. Fuse - the curvy line represents the part inside the glass that goes poof. Jack - the outer ring represents the part of the jack that usually goes to common or ground, the inner circle the signal carrier. Now they cant say you dont know jack. more VSAC 98 pics Now that we can give you color photos, I dug back through all the nice photos we received from VSAC 98 attendees. Tom Vetromile sent us the nice pic above, of the awesome Tube Research Labs amps and phono preamp built for Winston Ma. These babies greeted everyone in the show office as they signed in. Dick Olsher supplied the photo of a happy Ed Billeci and his Sato horn. Ed came away with a nice sampler of Audience caps as an award for his horn and the 250TL amp shown in 5/98 VALVE Dorothy Harwood of Acoustical Magic and Betty Kalmus of Antique Sound USA proved that audio is no longer just a mans game. Photo by Tom V. Ron Welborne introduced the new VV52BX powered Apollo amp kit, replete with beautiful chassis work, teflon sockets and a cool Japanese meter Photo By LynnO You have no idea what Doc goes through to get you a good price on MagneQuest iron Photo by LynnO Dan Meinwald and Alan Kafton set up a radical looking system in the EAR USA/Samahdi/Sahuaro room.Yes, those are speaker cables behind the Ichiban speakers and V-20 amp Photo by Tom V. So what are Eduardo de Lima, Lynn Olson, Gary Dahl, and the rest of the gang looking at? Garys Ariels in the Craftsman Room, of course. Photos by Hank Murrow These pics just barely scratch the surface of what went on at VSAC 98.Check out Lynn Olsons Ariel website, Dick and Leslie Olshers Black Dahlia website, and David Robinsons coverage of VSAC 98 in Positive Feedback, Volume 7 Number 6 for some other perspectives. So whens the next one? The superb quality of the exhibits and the major enthusiasm of the attendees has inspired us to make VSAC even bigger and better in the future. To give us a enough time to do it right, weve decided the next VSAC will be VSAC2000. Well put up info about where and when at bottlehead.com as soon as we have a venue and a date. By the way, in case you didnt guess, putting on a show of this type is a gigantic undertaking. If you would like to volunteer to help put on VSAC2000, give us a call. Wed love the assistance, and youd get to spend even more time involved in things tube audio. Entwined interconnect cable kits from Electronic Tonalities pre-cut twisted pair 20.5 guage High purity continuous cast long crystal solid copper conductors with a high temperature insulative coating, pre-cut polyethylene outer jacket and Vampire Wire RCA plugs $49 per 1 meter pair $10 each additional meter VALVE the magazine of astounding sound hardcore action - Buddhafied Afterglow Deep Throat - a Lowther front horn C4Sing the Decware Zen da’ basics - V=IR, it’s not just a good idea, it's the law! mo'’ Heavy Metal volume 6 number 3 1999 B-Glow single ended 300B amp kit another masterpiece from Electronic Tonalities active loaded 5965 driver MagneQuest TFA-204 air gapped output transformer 8 watts $900 the pair, you just supply the 300 Bs VALVE the magazine of astounding sound Editor and Publisher Dan "Dr. Bottlehead" Schmalle Chief Administrator “"Queen Eileen" Schmalle Resident Smart Guy and Technical Editor Paul "Braniac" Joppa Graphic Design Bruce "Badd Dawg" Borley Resident Hot Iron and Dr. B’s Bodyguard John "Smoothplate" Tucker Big gun OEM advisor Michael "Airgap" LaFevre The Guy W ith Answers John "Buddha" Camille Contributing Editors David "Full Track" Dintenfass "Crazy Eric" Lenius Our mailing address: VALVE P.O. Box 2786 Poulsbo, WA 98370 by phone: 360-697-1936 business hours: 9-5 PST, Mon -Fri fax: 360-697-3348 e-mail - [email protected] website - http://www.bottlehead.com VALVE in no way assumes responsibility for anyone harming themselves through exposure to the contents of this magazine. W e believe electrons flow from minus to plus, and that they can kill you along the way if you’re not careful. Vacuum tube audio equipment operates at potentially lethal voltages. Always treat it with respect. Many ideas published in this magazine are untried, and involve the use of potentially dangerous parts and tools. In attempting any idea or project published herein, you assume total responsibility for your actions and any harm caused to yourself or others. Please, be careful! This publication is produced as a service to the audio community and is wholly owned and published by Electronic Tonalities. The intent of this publication is to offer ideas to inspire and educate audiophiles in an effort to increase their understanding of the audio equipment they use and cherish. Blatant copying of the circuits published in this magazine for use in commercial products shows a complete lack of original thought. editor's thing Yo, bottleheadsDiscussion came up at the last meeting that while the new surge in local VALVE membership has been bringing in lots of folks who are eager to learn the basics of design, there seems to be a general swing towards requests for "cookbook" circuits in VALVE by the worldwide membership. (definition: if you read VALVE, you're a VALVE member, we are quite democratic) How can I put this diplomaticallyAin't gonna happen, no way, no how. For those of you who have recently discovered the pleasures of tube audio, and are finding a desire to construct your own gear, maybe partly for economy's sake (Amen, bro!), maybe partly for the satisfaction of telling others "I made it myself!", we aren't going to let you off that easy. See, VALVE was formed by a bunch of guys who didn't just roll tubes, or hook up a new piece of used gear every week. The guys who started VALVE learned early on to dig up the forgotten nuggets of information in arcane texts, apply that knowledge in their own experiments, and share that knowledge - not just the end result, but the method behind the madness as well. In fact the most hardcore DIY guys I know are usually more proud of their tube electronics book collection than they are of their projects! What we intend to present in VALVE is not just a canned circuit full of exact Digi-Key numbers and a preprinted circuit board, but rather a general design and just enough information to make you work a bit to get the project finished. This may seem a bit overwhelming the first time you work through a project published here, and that's part of the reason we’ve started "da' basics" column, to help you through the math and other basic knowledge you will use again and again in designing tube gear. You'll usually find the math to help you through the tough spots, and once you finish a project or two, our hope is really that you'll go off on your own, devise some devilishly clever new circuit, and share it with the readership (complete with color photos, of course). Which brings me to another important pointWe need article submissions like yesterday. We need not only your new circuit designs, but also your photos of finished ET kits and other projects, stories of your experiences learning the craft of tube audio, and your pieces on the theory of various aspects of design. You needn't be intimidated by the fanatical attention to detail of Buddha or the way math rolls off the pen of Brainiac. Some of our most popular articles are those like the original old S.E.X. speaker piece, where we slapped a couple of drivers on a cardboard box! And in fact I can't think of two guys to whom the sharing of knowledge is more important. Believe me, they will appreciate your contributions more than anyone, no matter what your skill level at the time of writing. So fire up the iron and the pen, but- don't let the blue smoke out, Doc B. on the cover Mike Connly sent us these photos of his S.E.X. amps. Mike not only built the amp kits and made the custom walnut and maple bases for the amps, he also made the chessboard upon which they rest. Mike was the first bottlehead to build a Blues Master, and rumor has it he will be putting the completed amp in a new chassis soon. Another cover girl, maybe? New exotica from First Impression Music FIM CD019 Favorite Chinese Instrumentals The Jin Ying Soloists 1 Like Wave Again The Sand (Pipa solo with ensemble) 4:36 2 Singing the Night among Fishing Boats (Jung solo) 4:15 3 Night (Percussion ensemble) 5:54 4 Love Song Of The Grassland (Tung-hsiao with ensemble) 2:34 5 Ducks Quacking (Percussion ensemble) 4:00 6 Love At The Fair (Er-hu solo with ensemble) 5:04 7 The Fishing Song (Bawoo solo with ensemble) 4:53 8 Happy Reunion (Xylophone solo with ensemble) 2:55 9 Chinese Martial Art (Emsemble) 1:43 10 The Flowing Stream (Er-hu solo with Yang chin) 8:25 11 Spenpadei Folksong (Yang-chin solo with ensemble) 4:32 12 Autumn Moon (Er-hu solo with ensemble) 7:06 13 Moonlight Over The Spring River (ensemble) 9:22 14 Variation On Yang City Tune (Ku-jung solo) 5:36 FIM CD020 A Vocal Tribute to Ben Webster Jacintha, Vocal Teddy Edwards, tenor sax; Kei Akagi, piano; Darek Oles, bass; Larance Marable, drums 1 Georgia On My Mind (Gorrell-Carmichael/BMI) 5:19 2 The Look Of Love (Baccharach-David/ASCAP) 4:08 3 Danny Boy (Traditional) 7:26 4 Somewhere Over The Rainbow (Harburg-Allen/ASCAP) 9:43 5 Startdust (Parish-Carmichael/ASCAP) 6:40 6 In The Wee Small Hours Of Morning (Hillard-Mann/ASCAP) 4:15 7 Tenderly (Lawrence-Gross/ ASCAP) 5:25 8 Our Love Is Here To Stay (George & Ira Gershwin/ ASCAP) 3:19 9 How Long Has This Been Going On? (George & Ira Gershwin/ASCAP) 5:28 10 Pennies From Heaven (Burke-Johnston/ ASCAP) 3:12 #189 16149 Redmond Way Redmond, WA 98052 http://www.fimpression.com Tel: 425-868-5326 Fax: 425-836-9061 Buddhafied Afterglow Hi Dan, Talked to Ken Dangerfield and he has been busy on the Internet. He told some group about the beefed up design I gave him for a two chassis layout for the Afterglow. (we had this info posted on the old website -B.) He has been getting numerous questions about the power supply, switching, noise suppression and CMCs. He came up with the idea of putting the mod on your internet site, so I cleaned up the drawings so you might scan them into the gadget. Evidently you are assembling a compendium of A-glow mods - pretty neat. Included a short theory-of-op’s to save you from a bunch of questions. Hope you do not find all of this too presumptuous. Regards, John C. Can you believe this guy? Too presumptuous? Zowie, this article has some incredible gems in it! Study these pages hard, learn from Buddha, and be a better builder for it! Doc B. the Deep Throat Horn a front horn for Lowther drivers by Bent Audio John Chapman of Bent Audio sent us these wild horns a few months back, and Doc just finally got around to setting them up. The tractrix expansion contour horns are molded from ABS and have a theoretical cut off frequency of 140Hz. The horn mouth is about 34" in diameter, and the horn is 18" deep, hence the name Deep Throat. The throat opening is 7-1/ 2", just right for fitting snugly against the frame of a Lowther driver. The driver mounts to a piece of PVC pipe which comes cut to just the right length to make a nice mounting flange, as seen in the picture to the right. John suggests attaching the flange with 5 minute epoxy putty, which worked nicely. The putty is rolled into a snake of a length approximately equal to the throat circumference and then pressed in the tapered gap between the outside of the horn throat and the PVC flange. Once the epoxy dried holes were drilled for 3/16" hanger bolts and the drivers were slipped on and secured with brass nuts and washers. The backs of the drivers were left open for the first audition, and fiberfill was piled over the backs to damp the rear wave. A quick and dirty frequency sweep by ear indicated that the horns went down pretty smoothly to 200hz, where they begin to roll off. Anyone who has listened to Lowthers knows they have a 'presence peak' which is generally centered around 2-2.5kHz. I have measured my PM2As as having more of a plateau from 2 kHz clear up to 10 kHz, so I was curious to see if these horns would fill in the midrange and upper bass. Yup! The peak is still there a bit, but the front loading does wonders for the balance without losing any of the speed and life that the Lowthers are known for. The dynamics are stunning, I have a drum solo that will blow your mind on these guys. I estimate overall sensitivity at something a r o u n d 101dB@1W@1M. I have been using a Whamo subwoofer temporarily, but we'll develop a woof that's a better match both in terms of bandwidth and sensitivity in the future. These babies may not be ‘plug'n'play', but they are really worth trying if you're a hardcore Lowther tweak. The Deep Throat Horns are $520 the pair, plus shipping. Contact John Chapman at Bent Audio, [email protected] or 604-533-6684 for more info. A similar horn called the Oris 150 has been developed by Bert Doppenberg. More info about it can be had at http://home.wxs.nl/ ~lowther/final.htm The Deep Throat Horns, at work in Doc's Chamber of Horrors and Kit Packing Dungeon Out wit h t he Old We are closing out the KR Enterprise VV Valves to make room for the new generation of KR tubes. All sale tubes below have the KR 1 year warranty from date of purchase. Visit our website for KR pictures, specs and curves. http://www.welbornelabs.com/krhome.htm Please Note: These VV Valves all have 2A filament current requirements. Please check your equipment specification before ordering and make sure they will operate in your amps. No returns on these sale items. VV300B...the following are all electrically the same tube, just different glass shapes and color. The cylinder tubes are just that...they have a cylindrical shape with a flat top. VV300B regular transparent glass $200 per pair VV300BL regular blue glass $200 per pair VV302BL regular blue glass $200 per pair VV302BC blue cylinder $200 per pair VV32B...these VV32Bs are all electrically the same tube except for glass color and shape. VV32B VV32BL VV32BC regular transparent glass regular blue glass blue cylinder all sold all sold $250 per pair VV52B...these VV52Bs are all electrically the same tube except for glass color. VV52B VV52BL regular transparent glass blue glass all sold Hurry, quantities are limited. All sales are final. all sold Buy 2 pair... take a 5% discount. Buy 3 pair... take a 10% discount. In with the New New From KR Enterprise. All tubes feature a 2 year warranty. KR10 Dual Triode Pre-amp and Driver Tube. A 6SN7 on Steroids? $395.00/pair KR2A3 Single-Plate Vacuum Tube A great new single plate 2A3. 2.5V/2.0A filaments. 2-6 watts of glorious sound. $395.00/ pair KR PX25 Vacuum Tube A replica from the past. 4.0V/2.0A filaments. 8 watts. $435.00/pair KR300B Vacuum Tube An awesome 300B replacement. 7 to 14 watts, 5.0V/1.2A filaments. $435.00/pair KR300BXLS Vacuum Tube 8 to 20 watts of power and dynamics. 5.0V/1.2A filaments. $575.00 per pair Welborne Labs ph: 303.470.6585 fax: 303.791.5783 http://www.welbornelabs.com e-mail: [email protected] New KR2A3 you asked for it C4Sing the Decware Zen By Doc B. We've hade several calls from folks who’ve been using the Decware SE84B Zen amp, a single ended SV83 amp manufactured by Steve Deckert (www.decware.com). A few of the callers have listened to the Zen amp and have asked us for a way to make the Zen sound a bit more dynamic. I point out here that the folks who have called liked the Zen amp, this article is not intended in any way to be a flame job of the stock amp. This mod is offered strictly in the spirit of experimentalism that makes VALVE what it is. The choice of tubes is cool - The driver is Svetlana's 6N1P, sister to the 6922, but with a bigger cathode and vastly reduced microphony. In fact we like the tube so well we are using it in a new prototype parafeed line stage here at Rancho Tonalities. The SV83 output tube is a sister to the 6BQ5, which any triode guy will tell you is the best sounding pentode made. the voltage swing requirements for the 6N1P are minimal. The circuit is as simple as possible, the only adjustment being a choice of cathode resistance on the straightforward voltage amp driver stage. The output stage is operated in triode mode with a 1K resistor tying the screen to the plate. To hit our numbers means replacing the 2.7K and 1.5K resistors with a single 833 ohm (820 is a common value that would be close enough) 1/4W resistor on each cathode. The simplicity of the circuit makes the C4S installation easy. The 6N1P is set up to run at a plate voltage of 156VDC with a cathode bias of 4.3VDC and a cathode resistance of 2.7K, or a plate voltage of about 104VDC, cathode bias of 2.3VDC and a cathode resistance of 964 ohms. The first operating point gives us a plate current of 1.6 mA, and the second operating point gives us a plate current of 2.4mA. Version 1 Looking at the curves published by Svetlana for this tube, these are really kind of low operating points. I'll do a conversion sticking with a low 2.4mA current first, and using the curves I'll shoot for an op point of about 110VDC on the plate and 2VDC of cathode bias. The SV83 grid is biased only 10V or so, so Our C4S's R1, the current set resistor, will need to be .95V/0.0024A, or 396 ohms 1/4W (390 is close enough). To set the bias resistors we will need to go back upstream in the circuit and figure out what our voltage should be at the top of the C4S loads and how to make it so. At point b in the power supply schemo we know we have a pretty stable 260 VDC or just a few volts less available. We will have a total draw of 6.8mA from our new circuit, 4.8 mA total thru the two plates and 2 mA total thru the bias diodes of the two C4Ss. The 15K and 10K resistor in parallel between points b and c equal a 6K resistor. The drop across this puppy at 6.8 mA would be 22.8V, so let's say we would have around 256 - 22.8= 233VDC available at point c. The actual value may vary a bit but this is close enough for jazz. two C4S loads with R1 = 390ohms R2 = 220K ohms each cathode resistor is 820 ohms to points “d” with C4S active loads version 1 two C4S loads with R1 = 95 ohms R2 = 120K ohms each cathode resistor is 200 ohms to points “d” with C4S active loads version 2 replace these two resistors with a single 1K ohm 2W wirewound resistor for version2 C4S loads replace 15K resistors with wire jumpers Now we calculate our bias resistors R2 on our C4Ss as 233V/.001mA = 233K ohms. A 220K 1/2watt resistor will do. Substitute wire jumpers for the 15K resistors between points c and d. The C4S loads replace the 47K plate loading resistors between points d and e, obviously... Version 2 For a higher current version that will have the 6N1P running at a point we like in other circuits we use, let's shoot for 10 mA at 200V as an operating point for our 6N1P. The SV83s draw a maximum of 66 mA total, so the total draw of two SV83s and the two halves of the 6N1P running with C4Ss will be666 + 20 + 4 = 90 mA, well within the maximum 150 mA current rating of the Hammond 372-FX power trans. R1, the current set resistor on the C4S board, will need to be .95V/.01A = 95 ohms. 10V of drive for the grid of the SV83. The cathode bias on the 6N1P halves will need to be 2V, so we need a cathode resistor on each triode of 2V/.01 mA = 200 ohms. We can now compute the value for R2. With 236V available at the top of the load and a 2mA current through the LEDs we need a 236V/.002A = 118K resistor rated for 1 watt. 120K is plenty close. Let's bump the LED's current draw up to 2 mA. We already figured our current draw by the 6N1P halves and C4Ss to be 24 mA. The voltage drop across that 10K and 15K resistor from point b to point c would now be 144V, way too much!! No sweat, let's just change the 10K and 15K resistors in our previously modified power supply (modified by the jumpers replacing the 15K resistors at points c and d) to a single 1K 2W WW resistor. This would give us 24V of drop, and our voltage at the top of the C4S loads should be about 260-24=236V. This is just enough plate to source compliance for our C4S load to work, and remember, we only need about What else can you do?? Parafeed it, Baybee Disconnect the secondaries of the existing output transformers, and cap couple a suitable PA matching type transformer, ala ParaS.E.X., to the plates of the SV83. Try a 2-3mfd coupling cap. The plate resistance of the SV83 may be a bit high with respect to the inductance of the Zen output-trannie-now-plate choke, so you may not get much sub 30 Hz bass, but there's only one way to find out, and it would be a cheap experiment..... B. da' basics V/I=R Ohm’s law the most important formula you’ll need Substituting 43 Volts for V and .060A (that’s the same as 60 mA, get it?) for I we get If you can remember this one, you can figure about 80% of the math out in a given circuit design. Ready? V=IR where V= Voltage I= Current R= Resistance How about some applications, you say? OK, here’s one: You need to calculate the value of a cathode resistor for a 2A3 self biased at 43 Volts and drawing 60 mA of current. We use our junior high algebra and rearrange Ohm's law to read Brainiac's Heavy Metal ...an occasional review of some nifty chunk of iron (usually cheap!) by Paul Joppa Today’s Topic: the De Young Mfg. S.E.X. kit “universal” power transformer P= 43V x .06A which equals 2.58 Watts. 43V/.06A=R which equals about 717 ohms. Now a nice feature of Ohm's Law is that we can relate power to it with the following formula P=VI where P = power and the other variables keep the same definitons. With this information we can calculate what kind of power rating our 2A3 cathode resistor needs. We know V = 43 Volts and I = .06A, so we can find P by substituting This is the transformer supplied with the S.E.X. kit for international orders. It differs from the U.S. version in having more primary windings so it can be wired for several power line voltages, it is rated for 50 or 60 Hz operation, and it has less B+ current capability than the Magnequest unit offered for the domestic market. It weighs about 3.5 pounds on my kitchen scale, and the lamination stack is 3” x 2.5” x 1.5”. The laminations are moderate, about 0.01”, and they are interleaved one by one. It is mounted horizontally with an upper metal end bell, and takes mounting holes 2” x 2.5”. All the wires come out on the bottom. The primary can be wired for 100, 120, or 240 volts and measures 7.1 ohms DC wired for 120 volts. There are four secondaries. The ratings and my measurements are as follows: Rated voltage 2 x 2.5v 6.3vCT 350-0-350v Rated current 2 x 1.25A 2A 60mADC Open circuit voltage 2.90 + 2.90v 6.67v 366-0-366v DC resistance 0.12 + 0.12 ohms 0.17 ohms 404 ohms CT By the way a good rule of thumb is that you want the power rating of a resistor to be at least twice ( the conservative say four times) the power radiated by the resistor. In this case you would want to use a 5 watt resistor at the very least, and a 10 watt resistor would be safer. There may be cases where you are working on a design and don't have one or the other of V or I through a given component, but you know the value of the resistor. You can still calculate the power rating. Since we know that V=IR, and hence I=V/R and we can substitute for I in our power formula: P=VI=VxV/R=V2/R or P=IRxI=I2R Cool, huh. Estimated voltage at rated current 2.66 + 2.66v 6.13 v 343-0-343 v* * the high voltage winding was estimated on the basis of 60mA RMS through the whole secondary, which is a reasonable approximation for capacitor-input circuits but is not exact. Leakage inductance was not evaluated but may reduce the B+ output voltage slightly. Equivalent source resistance in the B+ is about 267 ohms, or about 4% of the likely load resistance. With a capacitor-input filter and using silicon diodes, a maximum of 445 volts could be generated at 60mA. Remember however to allow for the drop in the DC resistance of any filter choke used, plus the loss in the rectifier tube if used. With a choke-input filter an output of 305 volts at 90mA could probably be obtained without excess heating, again minus the losses in chokes and rectifiers. Unusual in smaller power transformers, the regulation is pretty good. You can probably draw more B+ current if the filament windings are not fully utilized, but no more than half the extra volt-amp capability can be used this way without excess heating. jc morrison smashes record for the worlds largest S.E.X. speaker... This is a photo of one of a pair of speakers constructed by jc morrison and demoed at nyNoise, a very cool show put on in Hoboken, NJ by jc and pal Blackie Pagano, which we attended on March 13. The speaker is a 9' tall open baffle with 18 of the drivers that Doc worked with MCM Electronics on a couple years back (PN 551870). The tweeter is a Raven (sounded very nice!). There was also a TAD based subwoofer with this system. The overall sensitivity was quoted as 100dB, and it sounded like it. You long time bottleheads will note a basic resemblance to the open baffle S.E.X. speaker born from the unstable minds of Doc and Brainiac at the first VALVE Xmas party after several bottles of Champagne. If you want to take a project like this on, we might recommend that you try what is often called the "original S.E.X." drivers instead (PN 55-1290), With their high Q they are quite a bit more open baffle friendly, going lower on an open baffle (about 110 Hz vs. 200Hz for the drivers shown here) and a bit more efficient to boot. See our new Whamo webpages for lots more info. Thanks to jc and Blackie for great hospitality and a fun show. We hope to twist their arms and get them to come to the next VSAC. Hey jc, will those things ship? now that looks dangerous All you gotta do to get bottleheads to look at the camera is say "beer". Here's Smoothplate, John Hoffman, Brad Brooks (he's the one guy who’s working), Tom Vetromile, Richard Riley and Brainiac in his disguise, hard at work on the new VALVE listening room. Those joists that Tucker's almost hitting his head on will come out, and if you look close you will see the new ones he put in at 9-1/2 feet. The room will finish out to about 19' x 11'. We're planning on installing two layers of 1/2" sheetrock, and there's four hospital grade sockets on the front wall and one side wall, in case we audition speakers that like long walls, like Ariels. Oh yeah, there'll be a small wine bar in the back corner too. Brainiac smiled very wide when I announced this... Doc, This is Joe from Australia. Thanks for the Foreplay Kit with the upgrades. I have received the package in December last year. Unfortunately, I was away in Malaysia for a couple months. So, I was able to finish the kit just a few weeks ago. Anyway, I have managed to build another deluxe version of the kit using better parts like the Hovland musicap, Holco, Kiwame resistors. I have used VSE Allen Wright's voltage regulator together with the power supply of the Foreplay to provide the B+. Heater is also DC regulated as well. I have put the whole package in a Hammond Aluminium box with the valves sticking out proudly (see pic). I have managed to have a power transformer custom wound for operating in 240V country. I went to Octave Electronics (www.members.xoom.com/octave/) in Malaysia and they did it for me at a reasonable price (works out to be about US$27 / VA). So if someone from 240V territory needs the service, I would recommend them. Anyway, thanks again. Regards, Joe Ling Entwined interconnect cable kits from Electronic Tonalities pre-cut twisted pair 20.5 guage High purity continuous cast long crystal solid copper conductors with a high temperature insulative coating, pre-cut polyethylene outer jacket and Vampire Wire RCA plugs $49 per 1 meter pair $10 each additional meter VALVE the magazine of astounding sound Hawaii 5.0 two ways to play a RS 5"” driver mo'’heavy metal 300B taste test new Foreplay techniques Buddhafied Afterglow part two some ideas for SE 845 parafeed da'’basics determining triode plate loads volume 6 number 4 1999 B-Glow single ended 300B amp kit another masterpiece from Electronic Tonalities active loaded 5965 driver MagneQuest TFA-204 air gapped output transformer 8 watts $900 the pair, you just supply the 300 Bs editor's thing VALVE the magazine of astounding sound Editor and Publisher Dan “Dr. Bottlehead” Schmalle Chief Administrator “Queen Eileen” Schmalle Resident Smart Guy and Technical Editor Paul “Braniac” Joppa Graphic Design Bruce “Badd Dawg” Borley Resident Hot Iron and Dr. B’s Bodyguard John “Smoothplate” Tucker Big gun OEM advisor Michael “Airgap” LaFevre The Guy With Answers John “Buddha” Camille Contributing Editors David “Full Track” Dintenfass “Crazy Eric” Lenius Our mailing address: VALVE P.O. Box 2786 Poulsbo, WA 98370 by phone: 360-697-1936 business hours: 9-5 PST, Mon -Fri fax: 360-697-3348 e-mail - [email protected] website - http://www.bottlehead.com VALVE in no way assumes responsibility for anyone harming themselves through exposure to the contents of this magazine. We believe electrons flow from minus to plus, and that they can kill you along the way if you’re not careful. Vacuum tube audio equipment operates at potentially lethal voltages. Always treat it with respect. Many ideas published in this magazine are untried, and involve the use of potentially dangerous parts and tools. In attempting any idea or project published herein, you assume total responsibility for your actions and any harm caused to yourself or others. Please, be careful! This publication is produced as a service to the audio community and is wholly owned and published by Electronic Tonalities. The intent of this publication is to offer ideas to inspire and educate audiophiles in an effort to increase their understanding of the audio equipment they use and cherish. Blatant copying of the circuits published in this magazine for use in commercial products shows a complete lack of original thought. Yo, bottleheads, This issue I’d like to present Brad Brooks as our guest editor. Brad has been a local VALVE member this past year, and has really impressed us with his enthusiasm and commitment to the hobby. Below is Brad’s response to an inquiry by a newbie about learning the fine art of design, as posted to the Bottlehead ForumDon’t let the blue smoke out, D o c B. The following was posted by Scott Wobecke to the Bottlehead Forum: How long does it usually take a bonehead in math/construction skills to build tube amps? I have a lot of ambition...Which books do you recommend reading, I’ve come across some recommendations at the Audio Asylum. I figured if there is anyone to ask its the master of DIY tube gear. Thanks Doc. To which Brad replies: Here is my two cents. I agree with Quest that you should jump in and build something. Here is what I recommend, and please keep in mind that I do not consider myself a designer. I would like to think that someday I would be able to sit down with an idea, and find the right solution based on the combination of other people’s experience, my own experience, and research and experimentation. Here are some things that I have done to help me along this path. 1. Read, Read, Read—all you can about all aspects of stereo, not just tube, design. Decide for yourself what is funk, and what is bunk. Understand that alot of what is written out there is designed to sell products. Decide what your dream system consists of, and prepare to have your ideas blown apart. Develop enough character to deal with blows to your ego. 2. Decide what sort of music you really like, and what you really like about it. Calibrate your ear with live performances. Learn to love music again, unless you only like talk radio, and even then, learn to love the human voice. 3. Listen to as many different systems, tube and transistor, as you can. 4. Build something simple, like Electronic Tonalities kits, especially since there is enough information there to help you understand the operation of the circuit—in fact, pretty much all of the ET kits are made with the idea that you will continue to refine, redesign, and experiment. Learn by doing. 5. Listen to what other competent experimenters and designers say, and listen to how their systems sound. 6. Identify small milestones of accomplishment, experimentation, design. Small things, like how to determine the best operating points of a tube, or to find what design factors are affect bass performance. Experiment. 7. Continue to evaluate everything learned, experimented with, etc...throw out useless information and disproved theories. 8. Associate yourself with experimenters— people who actually like music and build the equipment that they listen to it on. Find a club of experimenters and music lovers. 9. Have fun, and ignore the bigots and jerks. 10. RCA Radiotron Designer’s Manual, 4th ed., 1950’s era Radio Amateur’s Handbooks, RCA Receiving Tube Manuals, Valve Online Magazine (Free!), Positive Feedback, Vacuum Tube Valley, Glass Audio. Sorry for rambling on... Brad on the cover Pictured this issue is the Foreplay preamp I decided to build for myself a while back, to try out some mod ideas I had. This preamp is now doing a tour of the staff at Audio Asylum, in our opinion the best audio forum on the web. In fact we think it is so good that we have decided to be a sponsor, and we are proud to announce a new Bottlehead Forum on the Asylum, in conjunction with this sponsorship. The forum will be a more timely way to get info out and offer answers to your DIY questions. Check it out at http://www.audioasylum.com/forums/ bottlehead/bbs.html new classics from First Impression Music FIM XRCD 022, The Artistry of Linda Rosenthal Linda Rosenthal, violin, Lisa Bergman, piano A collection of timeless violin solo favorites, by the most talented student of Jascha Heifetz with dazzling skill, dynamics and colors. You have to listen to believe. A must for demo. FIM XRCD 2000, Messiah by George Frideric Handel Yvonne Kenny, Paul Esswood, Martin Hill, Magnus Linden Members of the SWEDISH RADIO SYMPHONY ORCHESTRA THE STOCKHOLM BACH CHOIR ANDERS OHRWALL. Conductor Recorded live at the Adolf Fredriks Church in Stockholm, Sweden, on February 13 & 14, 1982 #189 16149 Redmond Way Redmond, WA 98052 http://www.fimpression.com Tel: 425-868-5326 Fax: 425-836-9061 Hawaii 5.0 by Gregory Hee and Jason Takamori The Weems’ Project In the mid-90’s, Hiroshi Ito began showing me literature describing triode amps, horns, and speakers claiming to play “music”. I was curious, but unwilling to plunk down $$$ for something I never heard. At the library I discovered a speaker building book by David Weems. No cutting edge stuff, but something caught my eye. Weems described a single driver project using a RadioShack No. 40-1354A 5 1/4" full range driver that “gets the midrange right”. Actually that’s all he said. Cheap enough. I picked up a pair to check out Mr. Weems’ hearing. I sized the box to my liking and built particle board enclosures from discarded shelving. He was right! With no crossover, dynamics weren’t restrained; no phase shifts, just music. Without hesitation, I built some real 3/4" MDF boxes. I surface mounted the drivers and applied a 1/8" cork sheet to the front. Kimber 8TC was used for internal wiring. Hardware was all stainless. The insides were lined with carpet pad on all surfaces. I would guess the response to be 60 to 15,000 hz. Perfect for my small room. Deep bass? Forget it, but then the highs are limited too. The sound is balanced. For 3 years, I listened in blissful secrecy. Enter Jason Takamori Then at a Jazz and Audio Society meeting, Jason showed up. He asked me what I had, but I talked about coherency and emotion instead. Soon afterwards, I invited Jason and Hiroshi over. It was the first time I let anyone hear my secret system. At one point Jason looked at his watch; it was past 1:00 in the morning. He kept saying, “It grabs you”. And this is through my B&K ST140. Jason asked me what else did I have going. Well, after my experience I purchased a pair of full-range Diatones that have been waiting for cabinets, but no further experiments with the RadioShack. They weren’t perfect, but aside from an Edgar tractrix horn TAD system with straight mid-bass horns, I hadn’t heard anything else that made me really want it. Jason’s Super Boxes RadioShack provided the motivation; the drivers went on sale for a mere $10 each. It was decided that the box needed to be more rigid and the drivers braced. Bracing was easy; a T-nut and a bolt with a wood plug through the rear of the cabinet sufficed. As for the box, Jason had other ideas, like 3/4" Corian. Yes, cast cultured marble would be more rigid, but he exercised restraint. His other deviation was to follow Weems’ design exactly. So how did it sound? “I can’t believe it’s . . .a RadioShack.” Music was clearer and dynamics were more powerful. Some of the upper midrange edge present in the MDF versions were gone. Jason’s Spicas went into his daughter’s bedroom. A few days later, Jason brought over a Corian version of my box (see picture and plans). They sounded wonderful too. The major difference is the larger soundstage projected by Weems’ large front baffle. My speaker presents a deeper front to back perspective. It is personal choice. By the way, the enclosures are heavy! Due to his 24’L X 16’W X 8’H room, Jason augmented his Corian speakers with two bandpass subs that Dan Schmalle de- signed for his Whamodyne project, powered by a Phase Linear 400. Upper frequency output from the subs is somewhat controlled by adjusting cabinet stuffing. The ShackAttack! Can a cheap speaker get better? Hiroshi calls it the ShackAttack. It started with 300 hz tractrix horns intended for Dynaudio D54 drivers. For fun, we put a pair of RadioShacks inside. The sound was awful. Removing the cabinet back was a transformation. The sound was effortless, smooth and big, but midrange detail was washed out. Adding a peizo tweeter to provide some “air” didn’t help, but the potential was there. So with the aid of Speaker Builder magazine and the internet, Jason and I charged forwarded. Following Dr, Edgar’s construction suggestions in Speaker Builder, Jason built a new 300 hz horn (no back enclosure). We couldn’t believe it. The midrange presence was back even though highs were rolled off as expected. Stereo images were deep and solid even 30+ degrees off axis. The horn mouth was still 14" X 11", but the throat was enlarged to 3 5/8" square. The drivers were mounted with a 1/4" gap from the throat. According to literature, this acts as a filter and will differ with another driver. Despite success, there was a hole between the lower midrange and sub, and images were a bit small. Thus our final iteration, a 240 hz horn to extend the coverage lower. We also modified the throat mounting board. The horns do what was intended and present a realistic soundstage even when sitting only 10 feet back. (See photos) Where Are We Now We still listen to the Corian projects. Be- ing a Lowther PM5A front loaded 140 hz round horn setup in Jason’s system, we needed to test the line between practical and extreme. It shows promise with lower distortion and more top end. Here and Back The RadioShacks turned out to be the key that allowed us to learn what the “to lust for” drivers do without breaking the bank. For a list price of $16.99 each, it is a bargain basement over achiever, in whatever project configuration you choose. Beginners take heart. Enough information is out there so that even a pair of novices can get started. Don’t blindly believe claimed efficiency. Crossovers can suck power. The 89 db rated RadioShacks in a box take less to drive than some 94+db speakers with crossovers. Build the box more rigid than you think necessary. You will hear it. Brace the drivers. Even the horn drivers were braced. Lastly, go for it. Aloha! sides working in smaller spaces, they “grab you” in a different way. Like the horns, they convey emotion. The horns by contrast are smoother and more effortless. The horns also spurred our quest for a better sub. Remember Schmalle’s beast is an under $100 project that needs no excuses. And the search is on for cheap drivers with lower distortion and a better high end. A 40 hz bass horn, driver by a JBL D140 coupled to a 6L6 bass amp now shares low end honors with the bandpass.. Are there any cheap drivers better than the RadioShack? We tried the 5" MCM driver used in the Whamodyne project. It is a good driver, but doesn’t work in horn application. We also tried kevlar, coated paper and poly drivers under $60. The performance of the kevlar driver was frequency dependent and never cohesive. The horn just magnified the plastic sound of the coated and poly drivers. Voices and instruments lacked the quality of being real. It appears that paper drivers rule. We also insertd the $300/pair Diatones which breaks the cheap rule, but after hear- Brainiac's Today’s Topic: the Allied 6K3VG power transformer This low-cost leader (only $22.95) is one of several in the Allied catalog. All are cheaper than their Hammond counterparts, but this one seems to be the best bargain of the bunch. It looks about right for hefty preamps or small (2-watt) power amps. It weighs 2# 7oz on my kitchen scale, and the lamination stack is 3” x 2.5” x 1.06”. The laminations are thick, about 0.025”, but they are interleaved one by one. It is mounted vertically with metal end bells, and takes mounting holes 2” x 1.75”. All the wires come out on one side. Heavy Metal ...an occasional review of some nifty chunk of iron (usually cheap!) by Paul Joppa Rated voltage 5v 6.3vCT 325-0-325v Rated current 2A 2A 40mADC The primary is rated at 117 volts and measures 11 ohms DC. There are three secondaries. The ratings and my measurements are as follows: * the high voltage winding was estimated on the basis of 40mA RMS through the whole secondary, which is a reasonable approximation for capacitor-input circuits Open circuit voltage 5,81v 7.35 367-0-367v DC resistance 0.224 ohms 0.305 ohms 500 + 468 ohms but is not exact. Leakage inductance was not evaluated but may reduce the B+ output voltage slightly. Equivalent source resistance in the B+ is about 600 ohms, or about 6% of the likely load resistance. With a capacitor-input filter and using silicon diodes, a maximum of 435 volts can be generated at 40mA. Remember however to allow for the voltage drop in the DC resistance of any filter choke used, plus the loss in the rectifier tube if used. With a choke-input filter an output of 300 volts at 60mA could probably be obtained without excess heating, again minus the losses in chokes and rectifiers. As is typical of smaller power transformers, the regulation is not the best, so be sure to add series resistance to the filaments if you don’t use the full rated current. You can probably draw more B+ current if the filament windings are not fully utilized, but no more than half the extra volt-amp capability can be used this way without excess heating. Estimated voltage at rated current 5.13v 6.45v 333-0-333v* 300B tube tasting By Paul Joppa At VSAC 98, one of the seminar events was a listening comparison of six different 300B tubes. This event came together almost by accident, starting with the realization that there were two or three types available in the local club. By simply calling around, several others were obtained - everyone was very helpful, and it is to the credit of this hobby that there is so much good will and enthusiasm on the part of everyone involved. The tubes tested were the following: The setup was a good ordinary system, except for the Exemplar speakers which were definitely a couple ranks better than the rest. A decent CD player was followed by a 5670-powered preamp. The power amp was the 300B-modified S.E.X. amp, running the tubes at 325v and 55mA through a TFA204 output transformer; the driver was a 6SN7 mu-follower coupled with a Hovland capacitor. Music was one jazz cut, followed by some symphonic Mozart - about one minute of each was played. Tubes were listened to blind the first time, then the whole was repeated after the tubes were identified. About 40 people were in the highceilinged room, of whom some 23 left copies of their notes. One major limitation of this test was the lack of warmup time. Each tube was operated for one minute before listening began. All but the AVVTs had at least several tens of hours on them, but all were cold when the testing started. This is thought to be a particular problem for the Valve Arts 5300 with its massive graphite plate. So as always, take these results with a few grains of salt! I would only add a statement that both the operating voltage and current were quite low and not optimized for any particular tube. (I know that AVVT definitely likes higher voltage and current). 300B “best” tube. But it did offer the opportunity to discover what kinds of differences were heard. As can be seen in the results, the range of perceptions was quite wide - in fact, one conclusion is that each person hears different things, and weighs what they hear differently, so that every tube sounded best to someone. But there is also some family character to each tube that seems to come out. (I’ll add my 2 cents too. The VA5300 was positively strangled at the op point used for this test. A more appropriate Valve Art tube would have been the C60, but these were not available at the time of the test. I’ve been using the VA5300 for several months now, at about 480V and about 160 mA, and it’s a big winner in my book - B.) 1998 Clearly there are too many confounding factors for this to be a test of which is the n Sovtek 300B, purchased from New Sensor by the author for the original version of the amplifier. n Western Electric 300B, a matched pair loaned by Charles G. Whitener of Westrex Corporation n KR Enterprise VV300B, loaned by Ron Welborne who was exhibiting at the show n AVVT AV302SL, loaned by Tony Bombera, the North American dealer for AVVT n Svetlana 300B, loaned by Eric Barbour of Svetlana n Valve Art VA5300, loaned by Ed Fallon Part One listening impressions I made several attempts to organize the listening comments, sorting them into groups by various criteria of similarity. None of them seemed to really help, and I continually worried that this approach was filtering other people’s perceptions through my own unconscious prejudices. Finally I gave up on interpreting the results. In the table below each row contains one listener’s comments. The only editing is that I’ve removed specific relative ranking comments. All comments on the sound itself are reproduced pretty much as they were written. Sovtek 300B Westrex 300B KR Enterprise VV300B AVVT AV302SL Svetlana 300B Valve Arts 5300 Natural, easy, pleasant Air; more HF Less air, nice mids, bass OK Soft, pleasant Nice air, mids natural, tight tuneful bass larger overall sound Lush, dynamic Soft overall, less air, mid OK, bass is fat not tight Open, detailed, but slightly veiled Nice air, natural decay of piano, full overall sound, bass a little recessed Very nice, dynamic Veiled, lacks sparkle, soft; bandwidth limited, listenable though. OK, not much top Quiet, articulate, Midrange good, nice bland overall sound Nice overall balance, highs tinny on occasion, lacks articulation Dulled transients but nice. Spitty. OK, nice piano & guitar, limited bass, sibilant treble, lack of air. Nice violins. Again nice piano & guitar better bass. Quite tight (faster) - better treble & good air Very good Fuller on piano, more detailed, faster Fairly good. Nice, mellow, smooth, laid back. Nasty sibilance, fuzzy, boomy Clear, smooth, balanced, not overly warm Involving midrange, lacking in bass punch, highs seem a little thin Nice sound Thin, not full sounding Nice dynamics, clear and lively. Somewhat blunt; More bass, same top Open, natural, some brightness at very top Warm, rich, clear Soft or slightly veiled mid, background could be quieter. Voices clear, brass grainy Good low end. Nice flow to the music Some bass punch Warm & rich sound, slightly less dynamic Good detail & dynamics, natural tonal balance, best of six Extended, clean, forceful, dynamic Pleasant but light weight Recessed but more natural, more depth, more open Drier piano, good guitar, treble not as good as #2 and slightly less air Dull but mids and drum good. Cymbals flat but pleasant. Limited bass; piano & guitar OK. - sibilant treble, not much air Bass less but good. Treble OK I like, good, natural. Can feel a little bass. Good piano & guitar, bass not quite there treble OK good air. Piano OK limited bass again - boomy piano, sibilant, OK air. OK Piano not as good as 2; good and fast though on instrumental A little less airy and natural but excellent dark dynamics Cool, not as engaging, but sounded accurate Clear highs, good detail but want more bass. Detailed voice, resolved violin OK Good piano, more sustain. Great pace on drum. I liked this one. decent Very good Piano murkier, more spurious sounding on instrumental less Slightly brighter Piano murky, OK instrumental, some lower mid peakiness boomy bass Cooler, OK Very nice tone; balanced Appealing, balanced Nice midrange, reserved top end. Voices could be more resolved. Balanced, good definition, quiet background. Nice vocal separation & violins. Not as involving. Could be more well defined. Soft bottom, good clarity Good balance top-bottom More up front & vivid that others --- Somewhat forward midrange Warm but mushy. Resentful sounding Overall average Very quick & detailed Muddy sounding Sweet fullbodied sound. Good dynamics Beautiful clear rich, good dynamic, human and Hollow & dry, mechanical. Good dynamic, no soul to it Sovtek 300B Westrex 300B KR Enterprise VV300B AVVT AV302SL Svetlana 300B Valve Arts 5300 Nice sound Good low end. Nice flow to the music Some bass punch Soft bottom, good clarity Good balance top-bottom More up front & vivid that others --- Somewhat forward midrange Warm but mushy. Resentful sounding overall. slightly smeary Overall average Very quick & detailed Muddy sounding Sweet fullbodied sound. Good dynamics Beautiful clear rich, good dynamic, human and soulful Very open. Hollow & dry, mechanical. Good dynamic, no soul to it Beautiful tone & clarity cooler & more neutral A little recessed and fuzzy. A very good tube. Thin, not full sounding Nice dynamics, clear and lively. Somewhat blunt; aggressive Blunt attack Warm & rich sound, slightly less dynamic OK, congested Slightly warmer; great clarity. Mids more involving. Good dynamics, impact & punch; open Thinner, less clean, less detail Very clean, natural inner detail Nice and clear good discernible detail - low & high better high Full bodied, forward a little, good bass and clarity Better balance, good dynamics About the same, a little more midrange Bright but not harsh. Good dynamics. Soundstage more forward yet polite, vanilla. Compressed, uninvolving, veiled. Forward, good Thinner still. Relaxed, quiet timbre, a little Smaller mellow, upper freq soundstage, rounded glary transients, good emphasis pace Very nice; a little Nice - maybe Very full more presence not as good sounding, clearer, more detail Good dynamics, tilt towards upper mids Good -?- White, bleached. Less dynamic. Good soundstage, less detail. Pretty good, fuzzier Good sense of depth, mellow, lighter bass but clean Thinner and less depth, lighter and airy, boring Good balance and clarity. Moderate bass and sweet highs Nice space and air. Clear sweet highs and snappy dynamics More lower bass but a little loose, more extended highs. Nice midrange. Bright Smooth. Mellow, more depth Lush, warm, Crisp, detailed, lacks bass, cold, shallow. mushy, soft, Dynamic, voices not clear voices layered, good on symphony A little thin in Lots of detail, a mids. Good little thin, crisp, frequency good tight bass range, fair bass. control, very nice Real good luscious sound. Slight upper midrange suckout. Less defined Good detail, bass a tad light Very good dynamic, good detail Balanced Depth, weight, definition Balanced Lush, warm, musical. Dynamic, voices clear, bass OK Sharp, harsh, voices unclear, bass mushy Sharp, harch, marginal bass, OK Good bass, good midrange, dynamic OK, not as dynamic Nice, bass good, musical. Voices not clear, not detailed on symphony. Full bass, dynamic, smooth, good frequency range No upper harmonics, no extended bass. Nice midrange. Easy to listen to. Clean highs but lighter bodied piano sound. Lighter bass, fine balance Very good, images well Different, good sound but some weird harshness, a little lacking in Sovtek 300B Westrex 300B KR Enterprise VV300B AVVT AV302SL Svetlana 300B Valve Arts 5300 Unremarkable, lacking detail Detailed, rich, nice high end Slightly edgy high end but detailed mids Nice air but slightly edgy high end Clear, good highs and natural sound Slightly edgy but otherwise good 300B tube tasting , Part Two - Tests on 300Bs After VSAC 98, I had six different brands of 300Bs on hand. I had to return two of them at the show, but four remained, and I couldn’t see returning them without making at least a few measurements to back up the listening tests. This article is the result. I had recently developed a test method which would allow me to find the plate resistance, gain, and the nonlinearity factor which I derived recently (see VALVE v.5 n.3-5). The method involves a simple experiment and a messy calculation. The experiment consists of powering up the tube in fixed bias with a plate resistor of about the normal load value, 2000-2500 ohms for 300Bs. Grid bias is varied from zero to cutoff, and the plate voltage and current are measured. The circuit is in Figure 1. Six or seven data points are more than enough. +300v - 400v ca 2000 ohms (variable) -150v Monitor plate voltage and current Monitor grid voltage 300B 50k ohms 16 ohm 5v 5v Fig. 1 - test setup. The calculation is a nonlinear least-squares fit of the data to my model of tube nonlinearity, in which current I is the integral of the 3/2 power law over a Gaussian distribution of gain: 1+3σ exp I( Eb, Ec, σ ) ( µ 1) 2 2 .σ 2.5.σ 2 .( Eb µ.Ec)1.5dµ 1-3σ Eb is plate voltage, Ec is grid voltage normalized to a m of 1, and s is the standard deviation divided by the average gain. The curve fit is done on equations of the form Ib K .I(Eb , Ec .µx , NLF) where the variables in the curve fit are perveance K, average gain i i i mx, and the nonlinearity factor NLF. I used MathCAD software to work out the fit. The plate resistance at a given current can be calculated from the perveance. This table summarizes the results, for both samples of each brand: Tube gain m plate resistance rp, W NLF Sovtek 300B 4.085 542 0.146 “ 4.079 563 0.141 AVVT AV302B 3.468 981 0.102 “ 3.733 862 0.105 Svetlana 300B 4.056 666 0.112 “ 4.018 645 0.116 Westrex 300B 4.034 631 0.117 “ 4.006 625 0.113 The AVVTs were not a matched pair, but the others were. As can be seen, matching was extremely good for all brands. Figure 2 shows a typical comparison of the measured current against the current from the model above; the fit is quite good. All tubes were run at 5.00 v rms on the filament except the AVVTs which were run at 4.80 v rms, at the suggestion of the retailer who so kindly loaned them (Tony Bombera - thanks, man!). 0.1 0.08 Predicted current 0.06 Measured current 0.04 0.02 0 80 60 40 Grid voltage 20 0 Figure 1. Predicted versus measured current A few comments can be made on these results. For one thing, the NLFs are not as low as I had thought they would be. This might be because of the AC filament heating, however - further study might reveal more about this. The AVVT tubes meet their claim of being more linear than any other, but they pay for it by having lower gain and higher plate resistance. All are still well within the expected tolerances relative to the nominal specifications of 3.85 gain and 700 ohms plate resistance. A few things puzzled me in the course of making these measurements. One was the high distortion of the Sovtek tubes, and the interesting results published recently in Vacuum Tube Valley where this tube was found to have better linearity if the filament voltage is lowered. So I tried running these tubes at 5, 4, and 3 volts, with these results: Tube gain m plate resistance rp, W NLF No. 1 at 5 v rms 4.085 542 0.146 … at 4 v rms 4.104 572 0.133 … at 3 v rms 4.151 653 0.114 No. 2 at 5 v rms 4.079 563 0.141 … 4 v rms 4.127 594 0.124 … at 3 v rms 4.090 737 0.079 It looks like I have confirmed Matt Kamna’s results - they do indeed get more linear at lower filament voltages. At 3 volts, the increased plate resistance suggests that this is not really enough filament voltage - the emission is really being limited - but it looks like they’ll run happily at 4 volts. Incidentally, I also listened to them in my amplifiers with about 2.8 volts on the filament, which is what I get in the 2A3 filament switch position - they sounded a bit cleaner to me, but seemed to run out of steam on loud passages. At 3 volts, the filament glow cannot be seen even with the lights off! The other puzzlement was that one of the AVVT tubes seemed to have limited emission. In order to get a good fit, I had to leave out the highest current test conditions. Figures 3 and 4 show the two AVVTs. 0.08 0.1 0.08 0.06 0.06 Ib Ib Ibx Ibx 0.04 0.04 0.02 0.02 0 80 60 40 Ec 20 0 0 80 60 40 Ec 20 0 Fig 3 - weak emission, Fig. 4 - strong emission While I was scratching my head about this, I got an email from Jim Dowdy asking if I would be willing to measure the nonlinearity of some AV300Bs that he had recently acquired. This was too good an opportunity to pass up, so I accepted gladly and he sent me ten of them for testing. The tubes were branded Audio Note, and older than the AV302SL’s that were tested above. This turned out to be quite interesting! On first testing them, I found that 8 of the 10 tubes seemed to have the same emission limit “problem.” To clarify this problem, I tested a Sovtek and a Svetlana 300B (both of which had been used for 20-100 hours). They showed no drift at all, and would draw 110mA at 80-90 volts with zero bias. When set to draw 150mA, reducing the filament voltage from 4.95 to 4.50 reduced the current to 145mA in both cases. Using the worst of the AVVTs, I found saturation at around 100mA - could not get more current no matter what the plate voltage. The saturation current varied with filament voltage, as follows: Vfil Isat 4.90 4.80 4.70 4.60 4.50 115mA 105 93 84 75 This confirmed that the problem was saturation. The current is proportional to the filament voltage to the 5th power, very closely. By now, I was getting worried - was there something wrong with these otherwise beautifully made tubes? Talking to Jim some more, however, he mentioned that he has seen these tubes drift a bit in current for the first 24 hours. So I burned two of them in, running a steady current of 70mA for a day and 150mA for another 12 hours on each. At the end of this treatment, the “problem” was completely gone! They showed no limitations at 4.80 filament volts, and could easily handle the full 200mA that my bench power supply is capable of. The first round of testing, before the burn-in, was done with 2500 ohms in the plate lead, and 350 volts supply. This gave about 100v at about 100mA with zero bias, ant of course 350 volts and zero current at cutoff, which was usually close to -110 grid volts. I did my curve fit at -20, -40, -60, -80, -100, -110, and -120v bias, leaving out the zero bias point because it was affected by the emission problem. Here’s the results: S/N mu NLF rp 1350 1398 1399 1418 1426 1445 1446 1456 1472 1484 3.51 3.76 3.45 3.72 3.58 3.72 3.72 3.69 3.66 3.67 .084 .136 .091 .123 .103 .128 .118 .152 .136 .124 903 798 965 779 880 825 811 836 804 815 I repeated the analysis leaving out both the zero and -20v bias points, but the results seemed to virtually identical, which I took to mean that only the zero bias point was affected. After burning in the worst two, I got these results: S/N mu NLF rp 1399 1426 3.67 3.75 .129 .130 851 776 Note that all the parameters are now very close to the averages of the other AVVT tubes. I conclude that these tubes simply need a good break-in period, at least 24-48 hours, before they will perform properly. They are tested at the factory for emission, but this is a pulse test which I suppose relies on the space charge more than the steady-state emission. The equivalent steady emission seems to be 80mA in the factory test, based on my reading of their specs. As for the parameters, the mu is on the low side (others usually measure about 4.0) but within spec and the plate resistance is on the high side (I’ve measured 700 ohms or less) but again within spec. The nonlinearity factor is about the same as all the other 300Bs I’ve measured. As far as I can tell, the only limitation on these tubes is their reputation (along with the similar ribbon-filament KR tubes) for fragile filaments, apparently due to the unavailability of truly high-purity nickel. (I do recall hearing somewhere that Westrex has a stash of filament nickel from several decades ago). Assuming that slow starting with a NTC thermistor and tight control of filament voltage to not exceed 5.00 volts will prolong the life, they should give fine service. Perhaps it would be wise to not turn them on and off too frequently, though. In any case, new production from AVVT uses a new filament with a core of stronger metal, which is said to eliminate the filament breakage problems. new strokes for foreplay by Doc B. After a fairly long run with the Soul Sister line stage prototype I decided I really should get around to finishing one of the eXception line stages for myself. Since this will be a bit of a project, involving the dismantling of the Soul Sister, and since I had given my demo Foreplay to Mikey after nyNoise, so I decided to whip up another Foreplay in the meantime. This would give me the opportunity to experiment with a few upgrades I had in mind. dress sexy Although a lot of Foreplay owners have spray painted the chassis plate, I had never tried one this way. I was really pleased with the black look of the powder coated B-Glow prototype chassis plate, so I decided to go for a black Hammerite. I did my trick of spraying on the stuff in mist coats, allowing each coat to dry before applying the next one, until I had built up a really nice pebble texture. pick ‘em up off the ground Before I sprayed the chassis I enlarged the RCA jack mounting holes to accomodate the nice gold plated jacks we use with the Glow kits. The holes were made large enough to allow use of the insulators so I could get my chassis to ground buss interface down to a single point, the center terminal of the terminal strip closest to the tube sockets ( terminal 13). Most of the assembly was done in the usual manner, with the Anticipation upgrade, natch. Our super cool 20.5 ga. high purity long crystal copper magnet wire was used throughout. dont snub ‘em, unless they deserve it. The first deviation was the incorporation of a “snubber” ahead of the bridge rectifier. See Buddha’s Afterglow article in this issue for a description of it’s function in a far more coherent way than I can offer. This filter blocks the reverse recovery spike of the UF4007 rectifier diodes, keeping it from reflecting back into the power transformer high voltage secondary, and subsequently the heater winding and the ;rimary, and back into your other gear. Instead of connecting the red secondary wired directly to terminals 4 and 5, a 10 ohm 2Watt wirewound resistor was attached to each terminal, and the secondary leads were attached to the free ends of the resistors. Then a .01mfd, 2kV ceramic disc capacitor was attached, one lead to terminal 4, one lead to terminal 5, effectively shunting across the output ends of the resistors. A second .01 mfd cap was attached across the input ends of the resistors, at the red secondary leads. Now the wiper ( center terminal) just serves to shunt the signal to ground, but the signal does not pass through it on its way to the grid. Cool, huh. You can retrofit this to a stock Foreplay. Just remove the wires that connect from more central pins of the selector switch to the right hand terminals of each of the pots. Now connect a 47K ohm resistor from those same selector switch pins to the terminal 2 of each tube socket. Don’t mess with the other components connected to the pots. choke them, but be careful take the path of least resistance The next trick was to convert the inexpensive 100K ohm volume pots to shunt operation. Thanks to Lynn Olson for this idea. Normally the signal from the selector switch connects to one end terminal of the pot. The other end terminal of the pot connects to ground, and the center terminal connects to the tube’s grid. The signal passes thru the carbon track on its way to the wiper ( center terminl) and the grid, not necessarily the highest quality resistive material. Between the power switch the power transformer primary I installed one simplified version of Buddha’s CMC filters to cut down crap coming in on the power line. See his article once again for the latest part numbers. I use 12 mfd 250VAC caps I had on hand and one of the CMCs that Buddha sent to Smoothplate a few months back. It was a shoehorn job, but I managed to get it to fit under the chassis. cap it off I’m pretty careful to tell anyone who buys a Foreplay that at $99 you’re not getting the best coupling caps ever made. Duh. I ended up leaving the great sounding Hovland 2 mfd caps that George Wright gave me in the preamp that I gave LaFevre. So on this one I put in the 3.3 mfd Solen caps we are now supplying with our parafeed amps. They were on hand, and ended up sounding surprisingly great for the price. In a shunt pot setup a 47K ohm resistor connects directly from the output of the selector switch to the grid of the tube. The end of the pot which would normally be connected to the selector is left unconnected to anything, and the other two connections stay the same. use the biggest thing you can lay your hand on Tucker came over one day a while back and braided me a power cord out of three 6’ lengths of 12 gauge solid copper wire, with a big ol’ yellow Hubble plug on the end. A total pain in the ass to braid, it makes your hands ache for quite a while afterward. We put it in in place of the hospital grade cord I’d been using for my big VA5300 amp’s plate supply, and the increase in bass punch had us just staring at each other goggle eyed( OK we was drinkin’ beer too). Kudos to Allen Wright for the original idea, in his Cable Cookbook. Natch one of these cords made it’s way onto the Foreplay. Well, the result is a very nice preamp. I lucked out to get a set of very unique Siemens ECC82s to use, which seem to have nickel plates! They are really fast and clear compared to my favorite 5963, although a bit lighter in the bottom end. A pair of TungSol 5963s proved to make a very nice sound too, although unfortunately my pair are hummers. To damp vibration I used one of Andy Bartha’s Whatchamacallits on the chassis right behind the tubes, and a pair of IERC tube shields. This really controls any microphonics. Had a chance to compare this preamp with the eXception at the last meeting. On Ed Fallon’s system, which was a bit bass heavy and mellow on the top end, I finally managed a one time miracle and beat out the eXception, with the Siemens’ ECC82s upper frequency emphasis being to the advantage. A couple hours later on Tucker’s eXemplars, the eXception with a 6N1P and a nickel output transformer was the clear winner, with lower distortion when driven hard. Ditto on my own system with the Lowther front horns and an eXception using the 5965 tube. Considering the difference in cost and sophistication, I’m pretty proud that the Foreplay stood up as well as it did. Give some or all of these mods a try. UPDATE Since writing this article I have developed a new budget stepped attenuator. See the next page for the story Sweet Whispers an affordable stepped attenuator kit from Electronic Tonalities At last, a stepped attenuator for less than $150. We have been asked many times over the past year for an upgrade to the stock potentiometers supplied with the Foreplay preamp kit (something like ”Gee Doc, if anyone can do a stepped attenuator for almost free, it’s you”). Some Foreplay owners have also expressed a desire for a more precise way to keep the dual mono volume controls balanced. So we decided to put together an attenuator that fit with the ratio of price to performance that the Foreplay offers, no small order. We eXperimented and came up with some minor compromises that would allow us to keep the price below $50 and still offer a substantial improvement to Foreplay’s sound ( yes, even over the shunt pot scheme shown in this issue). The difference in the cost of 23 position switches and 12 position switches is confounding. The best way to keep costs down was to reduce the number of steps from the typical 23 ( of which about half are never used in the typical preamp) to 12 (eleven steps plus a “mute” setting). The current switch does not have a stop at the lowest setting (something we are working on changing), but in practice this is not a big deal, you just need to stop turning when you hit the mute setting. To keep the attenuation range flexible the step size was set at 3 dB per step instead of the usual 2 dB. This seems to be of little consequence, we don’t find ourselves wishing for “in between” settings. In the process of determining the resistor values, we realized that we could solve a problem faced by owners of sensitive amps and speakers, that of ‘hair trigger’ volume controls that can’t be turned past about 9 o’clock before blasting. So the kit comes with two sets of resistors -a set that will give 0 to -30 dB attenuation for typical medium sensitivity setups, and also a set of resistors that will give -20 to -50dB attenuation, turning the Foreplay into essentially a unity gain preamp, similar in gain to a passive preamp. You just build the attenuators whichever way suits your system! Along with the mono switches shown in the photo above, we managed to find a reasonably priced two gang switch. And so you can order an attenuator kit to upgrade projects that contain 100K ohm stereo pots too. And another cool thing, they take about 20 minutes to build. You get a drawing that shows exactly where each resistor goes, and they install in a manner very similar to the stock pots. In a Foreplay you will just need to do a bit of rewiring of the ground buss once you remove the stock pots. We said less than $150. Heck, didn’t we say less than $50? How about $40, for ether a pair of mono stepped attenuator kits, or a single stereo attenuator kit. Doc takes care of your needs, baby... Buddhafied Afterglow part two by John “Buddha” Camille Several comments and questions have been received from the field concerning the Afterglow modifications published in CyberVALVE issue3. This modification was intended as a minimum cost enhancement to fit Ken Dangerfield’s needs of the time - not a double throw down killer amp with every trick known to man or beast. Evidently the beasts who analyze various circuit topologies with a background of audio rumor, heresay and superstition are hard at work saying it won’t work. Thus I will add a very slight embellishment to the theory of operation (editor’s note: this embellishment has come to me in the form of 34 handwritten pages - this is truly the short version where Buddha is concerned). I will leave it to the real experimenters to charge into the books to find out more about the whys and wherefores. This modification did little to the basic signal circuitry - a few tweaks here and there. A dual ground was added to make the amp compatible with a follow on total system design concept for low noise ( 100dB SNR vs. the 50-60dB SNR of most tube equipment). A minimum of filtering and line isolation was added to the power supply. Everything in these changes was driven by the parts availability at the time and the cubic volume available. I consider the amount of filtering and line isolation now provided as a bare minimum, totally brute force and very non esoteric. Esoteric spelled any other way is m-o-n-e-y. The power supply included a small percentage of solid state stuff to increase Ken’s familiarity with the three legged fuse world. The overall circuit is also safe in that it does not require a good scope, function generator nor various analyzers to debug. Experimenters should use the mod as a baseline, not an end all. Most parts values are not sacrosanct and in the main were determined while kitting the amp from various store shelves. Still this amp will outperform 95% of the amps out there, especially the store bought variety. Experimenters may try different techniques, parts and concepts at will - that is what valvedom is all about. Parts Availability Several parts listed from Tanner Electronics are no longer available. Local manufacturers and foreign travelers frequently wipe him out of the good audio stuff. 10 uF 250VAC line cap The super small 10 uF 250VAC across line rated caps were bought out by a local fabrication shop. A near exact replacement is DigiKey pn P9408 @ 10 for $39. Tanner carries a 10 uF 220VAC tubular for $1.99. This tubular does not have the form factor of the 9408 nor is it rated for across line service, but is still legal since the primary circuit is fused. This capacitance value is also not magic, see the FL2 theory. Relay K2 was spec’d with a 9V coil vs. the actual 10V coil. Ask Tanner for the deer feeder relay. 3K32 20W 2A3 cathode resistor This mil spec chasis mount resistor of around 3333 ohms biases the 2A3 to a little over maximum rated plate dissipation, about 15.5 Watts vs. rated 15 Watts, assuming a 425V B+. To maximize tube life increase the valus of the cathode resistor to 4K. Use Ohmite type 270/ DigiKey pn L25J4K0. This value drops the plate dissipation to around 13.5Watts. Another option is to use a 5K adjustable power resistor to set the plate current. Use Ohmite/ Memcor style AR25/Mouser 588-AR255K. Dont forget mounting brackets. the adjustable resistor will allow exact setting of plate curent and thus plate dissipation to your local operating conditions. UF4007 Tanner’s has had a run on his UF4007 diodes. These diodes are available at both Mouser, pn 625-UF4007. $0.25, and DigiKey, pn UF400DICT , $0.74. Am testing a new Phillips diode, BYM26E, that may be a cheap replacement. .01uF 6kV disc cap Parts Additions/Comments The .01uF 6kV caps are no longer available at Tanner’s. He has a quantity of .006uF 3kV disc caps that will work well in this application. Also see PN Reverse Recovery Filter. MOV addition K2 errata Somewhere along the way two protective MOVs were deleted from the power supply drawing, sheet 4. MOV1 should be added in parallel with the fourth 10 uF cap following CMC3. MOV2 should be added in parallel with the primary of T-2. Use Panasonic pn ERZ-V20R201/Digi-Key pn P7322 ($0.72). Contrary to popular belief, I add MOVs to the primary circuit after all filtering for several reasons. One, the line filter reduces the slope of the dv/dt rise from line borne impulse transients thus allowing the MOV to clip earlier in the transient cycle. Two, placing the MOVs next to each transformer permits tighter clipping of the inductive kick back of the transformer upon shutdown. This kick back transient is the usual cause of solid state failures on the down stream side of the transformer. Also, see On MOVs. CMC change The Panasonic common mode choke (CMC) special for CMC 1 thru 5 is spec’d at 4.7mH/4A on the crates at Tanner’s. I noticed that the CMC pn ELF-18D850B is now spec’d at 3.3mH/4.2A in the latest Digi-Key catalog. The CMC will probably meet both specs but I wanted to eliminate the confusion. Tanner also has a TDK pn 472Y4R0t CMC rated at 4.7mH/4A. Both CMCs are less than a buck a piece. I prefer the TDK. Relay K2 substitution The specified relays out two sets of contacts have been used to switch secondarty circuits at voltages up to 400VAC above ground. However, this has only been done in conjunction with primary power switching, done here with K1. The contact point spacing may not hold off stepped up line transients if the transformer were constantly energized as in some other applications. Circuit changes or substitution of another relay may cause problems so check it out. Rather than dragging out my hi-pot supply, I kludge up an AC supply and let it run for several hours per contact while doing something else. This technique allows possible carbon tracks or other insulation failures to develop. Blow the relay here, not after it is installed. Discharge Diodes Delete the discharge diode D1 between C2 and C3. This diode was originally used to discharge C3 in order to prevent magnetization of the OPT core duriong shutdown. However it has been found that resonant effects can develop significant AC voltages with some secondary loads on the OPT. Thus diode D1 may become forward biased during part of the AF cycle causing clipping. Diode D1 is replaced by a realy circuit that will prevent OPT core magnetiza- tion from both charge and discharge currents to C3. See Demag Prevention. Add a UF 4007 discharge diode between C1 and C2, see the drawing. This diode speeds the discharge of C1 during shut down. I mentally miscomputed the time constant of C1 (1500uF) and the cathode resistor (3320ohms) at around 2 seconds, vs. 20 seconds (25 actual). My power of ten neuron dropped a digit. This fix will decrease cathode stripping in V1. Bypass Cap C3 Change the voltage rating of C3 to 600630 VDC. This change will provide a slightly better safety factor against low frequency resonance effects and the resultant high voltages that can be generated across C3. the experimenter should be aware thet the load on the secondarty of the OPT has large effects on the amount of voltage generated on the primary. A momentary disconnect of the speaker load will cause extremely high voltages to be generated by the series resonant circuit, more than enough to break down the insulation of C3 and possibly the insulation in T1. Of course this failure mode will occur only if the load is removed when a low frequncy near resonant signal is being amplified. It is also concievable that a speaker having low frequency resonant Z peak in the 10 to 30Hz region may cause the same problem. It might be wise to measure the AC voltage across C3 with your normal speaker load while playing a series of low organ pedal notes or a test record, to see what happens. Fortunately for most pocket books, most SE speaker systems are resonant at much higher frequencies, mitigating this problem. This resonance problem does not affect systems that use very large value of capacitance for C3 where series resonant effects are well below the magnetic capability of the OPT. Manual OPT core magnetization prevention Add a manual magnetization prevention circuit, see drawing. This circuit adds a realy and manual switch to short the primary winding of the output transformer during turn on and turn off cycles. The idea is to prevent magnetization of the OPT core by the virtually DC charge and discharge currents of C3. I found that these DC currents caused measurable ( visible on the scope) magnetic saturation effects within the nickel OPT in a tuner I was developing for bottlehead Bruce Nilson. An automatic demag circuit was developed for the tuner but it is too complicated for this basic amp. Thus the manual circuit is recommended. It will prevent core magnetization and should provide faster “warmup”. I found that it took almost an hour for the tuner’s MagneQuest B7 line transformer to “clean up” with a 20Hz signal at normal output - 1VRMS. At full output , 5.5V RMS, the transformer still required several minutes to demagnetize. effective. The FL1/FL2 combination reduces line borne noise fairly effectively in a relatively small volume and is dirt cheap for the isolation provided. Second, the network is also a rough approximation of a linear transformer that reduces the AC RF line impedance significantly. For the experimenter with CAD capability, FL2 can be optimized using modern network filter theory algorithms such that the output impedance is a sub multiple of the input impedance. AC powerline RF impedance normally runs in the 100-150 ohm neighborhood This impedance can be halved or quartered without too much trouble. the L’s and C’s can get pretty big volume wise, however. While you’re at it, put a notch at 180Hz where the worst noise side band usually exists. Why did you do that’s? FL2 The network consisting of CMC 1 thru 3 and the four 10mfd capacitors serves several functions. First, the network serves as a low pass filter that starts rolling off at several hundred Hertz. FL2 is effective to well over 50 kHz where the line filter FL1 starts becoming Thirdly the filter FL1/FL2 smooths rectifier current impulses that travel back down the power line to low level stages in the audio system. To be facetious, we are trying to simlulate a kilobuck line cord here. A general rule of thumb should be intuitively obvious to the most casual observer - if you can hear the effects of a line cord you need work on your power supply. Schottky diodes for BR1 Using Schottky diodes for low voltage high current supplies virtually eliminates the noise generated by pn diodes. The often recommended high current bridges commonly called out for filament/heater supplies generate seious amounts of reverse recovery noise. These high energy noise transients are virtually impossible to filter. Since Schottky diodes have essentially no minority carriers they produce very low level diode noise spikes. these low level spikes are readily removed such as is done with CMC4. Schottky diodes also have roughly one half the voltage drop of pn silicon diodes, thus greater headroom is usually available to down stream regulators. RLC filters for HV rectifiers The pn silicon diodes used to rectify the high voltage B+ power generate a significant reverse recovery spike ( actually a damped wave with a very high initial pulse). The specified UF4007 diodes from Tanner’s have a pretty clean recovery spike - comparable to HEXFREDs. In fact in several installations I have found the UF4007 easier to filter than the HEXFREDs faster recovery spike. At any rate, brute force RLC filter networks on each side of the rectifier diodes attenuate these spikes significantly - usually down to the millivolt level. The filter formed by CMC6 and companion capacitors further drop the 10-20mV spike train down into the noise. NOTE: the filter/diode networks should be assembled using extremely short leads, RF style, preferably on a perf board with a ground plane. In this supply all HV parts from K2 thru the third 470mfd cap can be mounted on a proto board available from Tanner’s. Ask for the TI puddle board. Of course the smoothing chokes L1 and L2 are chassis mounted. Twist and shield leads to the board from T1, L1 and L2. Shields should be returned to the ground plane that in turn is returned to the chassis through 3/8 inch stand off spacers. All small parts should be mounted on the solder side of the board and thus shielded between the ground plane and the chassis. Also, ground plane clearance holes should be countersunk slightly with a 1/4” metal drill (120 degree rake) where HV leads pass through the board. Deflux the board and shoot with several coats of clear Krylon for added safety. ( Dang, Boss, and this is the quick and dirty method???!! - B.) The L ( inductance ) portion of the above filters is provided by the use of 10 ohm wirewound resistors available from Tanner’s. Alternatively a 1/2W carbon film or carbon composition resistor may be close wound with #34 magnet wire. This method is much less effective than the small wirewounds. Be sure the first color code stripe is double width, signifying wirewound, when purchasing. B+ discharge circuit B+ may be conveniently discharged very quickly (<2 seconds) by utilizing the center normally closed contacts on K2. NOTE: observe the schematic and tie the 150 ohm resistor from the B+ buss to relay lug 2, not lug 8, which should be grounded. The primary reason for this circuit is to rapidly discharge the HV buss in order to reduce cathode stripping as the filaments/ heaters cool after shut down. Tubes are not a quarter each anymore and the total additional cost of this mod is around 25 cents. In addition the discharge circuit will probably be exercised a hundred times during the debug and will no doubt save several skinned knuckles. Lastly, a bleeder that draws adequate current (10%) will dissipate another 4.5W of under chassis heat ( 40Kohm resistor) and take 5 minutes or more to drain the HV buss to safe levels. C4S diode Why place the back biased diode across the C4S for V1? Probably not really required for this particular circuit but it has been found necessary in other circuits, especially RC coupled stages. I recommend using the diode on all C4S installations. Here’s why: The C4S has been tested and used by the author and others in various installations and has been found to be very robust. However some field installations have popped the driver transistor several times. This high Beta very small structure transistor does not like back bias currents of more than a few milliamperes. This current can be generated by several mechanisms. The most likely mechanism in this installation is arc back between the plate- grid structure of the 2A3. Arc back is self clearing and usually goes unnoticed but happens periodically, especially in new tubes. Small particles of filament/cathoe coating and other foreign particles and debris break loose and may be propelled by electric fields to a point where the arc occurs. this arc back biases the C4S and the transistors avalanche. This avalanche current is too much for the fragile high gain driver transistor. Another failure mode occurs when the C4S is used to feed the plate of an RC coupled stage. The charged coupling cap back biases the C4S on shut down and once again the avalanche current may pop the three legged fuse. Other failure modes are out there, including hameous fistus, but the UF4007 should be fast enough to correct the problem. L1 and L2 filter chokes A swinging choke is not necessary at L1 since this application uses a capacitor input filter. thus the output voltage has already soared to its maximum values. Also, the current load of this amplifier does not change appreciably - alleviating the reason for a swingin choke, even with a choke input filter. Critical inductance for a choke input filter is about 7Hy for this amp. The specified chokes have more than adequate inductance and current capability and could serve in future mods. The 100ohm DCR is an important factor here due to low B+ overhead. Why not regulation? Voltage regulation was deemed unfeasible in this mod for several reasons: 1 The power transformer plate winding does not have adequate voltage output (headroom) for a series type regulator. 2 The plate winding does not have an adequate current capability for a shunt regulator. 3 Inadequate room on Ken’s chassis. 4 Experience and test equipment availability. A first time layout on virtually any regulated power supply I have ever built has always oscillated. Other folks seem to have the same problem as several regulator kits and commercial “store bought” amplifiers I have checked also oscillate or go into a limit cycle mode. One popular solid state kit regulator has had a limit cycle oscillation at between 90mHz and 210 mHz on the three systems I have been asked to look at. The limit cycle mode, manifested by a 1V to 10V RF signal riding on the B+ DC voltage, can only be dtected with the proper equipment such as a good fast scope. Cleaning up the limit cycle removed the hard edge on the amps involved. A popular all tube regulator making the rounds also hs a limit cycle pulse mode at several hundred kHz. The pulse train rides on parts of the 120Hz output. The 120Hz output of a volt or so was due to the extremely low bandwidth of the basic regulator circuit - DC to about 10Hz. It is hard for an error amplifier with a 10 Hz bandwidthto correct the 120Hz hum input to the V-reg. To be truly effective, a regulator circuit must be faster than the load that is regulated. If your amp rolls off at 40kHz, a good rule of thumb dictates a 400 kHz bandwidth for the regulator - this is hard to do. Add a wideband noise requirement of less than 100 microvolts and a low dynamic impedance and the problem really gets hard. To get the gain/bandwidth for these two requirements is at the limit of the state of the art for solid state, virtually impossible with valves. This hard to do problem might explain the complaint of most folks that my power supplies are much too complicated so they press on with their hum, hiss and turtle slow systems. At any rate, getting back to test equipment, get yourself a surplus TEK 7704 or 7904 scope and at least a 7A26 vertical plug in (200MHz). 7904 mainframes are around $200 in this area. This setup will get you through 90% of the V-reg development problems. That 5 mHz scope might get through most audio amp problems but will not be fast enough for the power supply. Hopwever, that hard sounding 6922 preamp might also be oscillating at 400 mHz... Grid stops The majority of amplifier stage oscillations can be cured with a grid stop resistor. High Gm tubes ( over 2000) love to oscillate and at some frequency virtually any layout will become a tuned plate, tuned grid (TPTG)oscillator, see a 50’s ARRL Handbook. The simple expedient of placing a grid stopper at the grid lug of all tubes will usually stop the TPTG oscillation effect. When I say at the grid lug, I mean at the grid lug. If you are of the screen grid valve persuassion, a grid stopper should be used on the screen grid lug, especially if the screen is returned directly to ground through a bypass cap. Also, do not take the shortcut of tying other leads to the grid lug. The only part soldered to the grid lug should be the grid stopper. Plate stops ( not used here) On several recent occassions I have observed VHF/UHF RF oscillations between 200 and 400 MHz in commercial 6922 voltage amp stages. The layouts were ideal for an Rf oscillator, with relatively long (>1 in.) leads or traces to both the grid and the plate of the 6922, a really hot tube for RF work ( for which it was designed). The first amplifier was stabilized with a real stopper. The real grid stopper was kludged into the circuit trace next to the grid lug between the original film grid stopper ( ~1.5 inches away) and the tube. Remember, a lot of film and bulk foil resistors go inductive above 50-100 MHz. This circuit them became unconditionally stable over the audio cycle and sure sounded better. The second amplifier calmed down with a grid stopper placed into the signal lead at the tube’s grid lug. It did not oscillate continuously, however the circuit would break into a very low level RF oscillation during a portion of an audio signal - a most common problem, dude. this oscillation was killed with a 51 ohm 1/8 watt carbon comp resistor between the plate lug and the “noninductive” plate resistor. For starters, there is no such thing as a noninductive resistor. At some frequency the so called non-inductive resistor will start showing a significant inductive reactance. If the tube and associated circuit has sufficient gain at that frequency it will oscillate, especially a high Gm frame grid tube. This greatly simplified explanation is meant to alert experimenters to the fact that many things are going on in even the most mundane circuit. Layout and parts selection are critical and every change should be evaluated. fortunately a critical ear can detect when a change makes the sound better or worse, but a new circuit may be discarded out of hand for a subtle reason that may only be betected with proper test equipment. Note: the above part cycle oscillation only occured when the plate swing went over 10V p-p. the spurious oscillation was of a very low level , only 100 millivolts or so at the frequency of around 150 MHz. This appeared as a very slight thickening of the CRT trace during the most negative portion of the 10V p-p, 1 kHz plate swing. A high pass filter was kludged out of a 1 pF cap and a 10 microhenry RFC at the tip of the scope probe to better oberve the VHF oscillation, i.e. to get rid of the 1kHz signal. The oscillation would also be killed when the scope probe was connected to the affected stage. This phenomenon occurs frequntly, so the search for spurs can be conducted by holding the probe near, but not touching, various terminals. Of course the scope should be set to one of the more sensitive positions e.g. 5mV/div. with the X10 probe during spur searches. Never use a X1 probe due to bandwidth limitations. The lessons here are that virtually any active circuit can amplify and oscillate at the same time, or oscillate at several frequencies, or any combination of the above. The famous hard sound of the 6922 is a typical example - it is usually oscillating. Also, suspect those very neat layouts where all parts are neatly aligned with leads or traces meandering all over the place. those nanohenries and femtofarads turn into nice VHF-UHF tank circuits. Speedup resistor Why the 82 ohm resistor in series with the diode across K2’s coil? In the old days this resistor was called the speedup resistor the physics of which I won’t go into. As used here, this resistor speeds the release time of the associated relay. this reduces contact arcing to some extent and in this case to 1/4 cycle or so of the 60Hz supply due to pulsating DC nature of current flow. I generally use a resistor value that approximates the DC resistance of the relay coil. This value halves the value of back EMF current flow upon shutdown, reducing the relay armature magnetic hold force significantly. The down side is that the back EMF voltage spike generated is twice the relay coil voltage vs, approximately 0.7V. In this case approx. 16V. The 16V pulse is no problem for the PN2222A that is good for 60+ Volts. The 16V pulse might back into the 8V buss and damage the 555 but this pulse is clipped at ~ 12V by the 12V TVS. This is a side benefit of the TVS whose primary purpose is to clip line borne transients on the 8VDC buss. A tertiary purpose of the TVS is to clip the shutdown transient pulse from K1. Easy Tweak ( editor’s note: gasketing the bell ends as described below will void the warantee on MagneQuest products. We are not saying it won’t work, just that you are risking dropping and stressing the unfastened core far worse than stresses described within this next section - proceed at your own risk) Permalloy, mu metal and other high nickel ( Ni) cores must not be stressed mechanically for optimum results. High tech cores are enclosed and floated in silicon grease or very compliant elastomers such as silicon rubber. The enclosure prevents winding stress to the core material after heat treatment thus maintaining the magnetic qualities of the core metal. The experimenter can relieve future stresses by proper mounting techniques. If the transformer is rigidly mounted to a chassis differential expansion rates will keep the core under a constant state of stress during operation. This tweak will prevent these stresses from building to typical levels. This tweak will also produce audible results on silicon steel cored transformers. Mod Procedures 1 Remove the bell ends of the transformer. If the assembly bolts are steel, replace them with threaded brass rod. 2 Fabricate two rubber gaskets taht will fit between the bell ends and the core.I use the soft neoprene gasket material sold at hardware and auto parts stores.These rubber sheets are .020 to .030 inch thick and are dead soft and pliable. The idea is to prevent any machanical contact between the bell ends and the faces of the core ma- terial. 3 Cover the transformer assembly bolts/rods with shrink or vinyl tape over the portion that passes thorugh the core. Prevent mechanical contact between these bolts/rods and the core material. 4 Reassemble the transformer, ensuring that lead wires and gasket material are properly positioned. Tighten all nuts finger tight. 5 Draw all nuts down evenly using a nut driver. Draw down should be done in several stages using crisscross sequence like the auto wheel lug torquing method. Final torque should only be 6-8 inch pounds. 6 Degrease the transformer assembly and shoot with several coats of clear Krylon. This clear coat will stop the slight shock one will receive from the core or the bell ends during operation. The shcok is caused by the now totally isolated core rising to around B+voltyage due to electrostatic forces. Older paper insulated transformers should have a drain wire ( small, stranded, tinned copper) inserted between the rubber gasket and the core. The drain wire should be returned to the amplifier chassis ground. 7 Mount the transformer using nylon hardware and shoulder washers. Drill mounting holes so that several thousandths of lateral play exists between washer shoulders and the chassis. Add plain washers as necessary between shoulder washers so that several thousandths of vertical play exists between each shoulder washer set and the chassis. The transformer should be free to move several thousandths both vertically and laterally afetr all nut/bolt sets have been torqued to 8-10 inch pounds ( 8-32 hardware). After final assembly and debug, the nut/bolt sets may be RTV’d for long term security. On MOVs I have been using MOVs on every piece of gear built or overhauled since 1975 when my house in Tampa received part of a lightning strike to a nearby pine tree. Most of the stroke went directly to ground through the tree as evidenced by the complete debarking of the 10 insh caliber tree. Part of the stroke went over to the house through several dozen roofing nails and thence into the house wiring. My brand new (1 month) solid state Heathkit TV and every piece of ham gear using FETs were damaged. Also every motor in the house including the AC compressor plus water heater and stove heating elements were zapped. While at Graingers buying new compressors for the AC and refrigerator, plus all those other motors, a prominent display of GE Thyrite surge suppressors caught my eye, so I bought several. In addition GE MOVs were starting to appear in electronic parts houses, so I got a hand full of those. I placed a Thyrite across the electrical service entrance, across the breaker panel, the Ac compresor and the AC airhandler. 20 joule MOVs were placed across all other motors, all appliances, and all electronic equipment. A year later alomost to the day my ham antenna mast took a direct hit - a portion of which got into the houe wiring and vaporized the innards of the power meter. Also had a lightning ball bounce between the AC grills in the living room, so plenty of energy entered the house. The only damage suffered during this second hit was to the masthead preamp where the helicoil front end filter was vaporized along with that new $40 FET. Since that time I’ve treated each new house the same way, thyrites and MOVs across everything. Four or five years ago the present house took a hit ot the chimney mounted TV-FM antenna. the only damage suffered was the vaporized balun between the antenna and the masthead amp. A coax spark gap suppressor even saved that super lo noise transistor in the front end of the mast head amp. I have yet to experience any of the ills suffered by several writers in recent audio rag articles. Even if i did suffer a MOV failure or two I would really be happy. That six bit sacrificial lamb went down fighting and savd me a thousand bucks of bitching and moaning while fixing damage. The gradual degradation of MOV devices has also not been noticed. Maybe this is due to the dual layers of protection offered by the Thyrites and several dozen MOVs across the line at any one time. Initially I used to measure the breakover voltage on MOVs installed in test equipment undergoing calibration. No observable increase in breakover had occured in many samples so I quit the practice 5 or 6 years ago. I still check the MOVs across the fridge occasionally and no deterioration has been noted. This compressor motor produced up to 6 kV pulses on each shutdown.These spikes are reduced to about 1kV with the MOV protection. GE Thryrites are code in the US and Canada and are available at the nearest GE supply. They are called “Traquell surge arrestor” with pn 9215ECB001 at $60 - 70 each. These deviced are easy to install in a convenient knock out or can be suspended by the elads in breaker boxes, etc. Keep leads short and straight, one black lead to each side of the 220VAC line and the white lead to the neutral block. MOVs should be connected across the line and from both line and neutral to ground in major appliances and other high dollar equipment. For the small stuff, place one across the line, line to neutral. On inaccessable gear such as the fridge and microwave place the 3 MOVs across the back of the wall receptacle. the EXO-50 “What this country needs is a good 5 watt 845 amp” Mike LaFevre, MagneQuest Here’s a neat design idea Paul Joppa whipped up in an evening, after an e-mail from Doc. The basic premise was to do an 845 amp using the PGP 8.1 power trans, and the EXO-50 parafeed output transformer. Here’s what Paul came up with “With a full wave bridge and a choke input filter you can get 630VDC minus the choke losses, at 60 mA. This is workable, a 5800 ohm load is optimal so the 5K EXO-50 should work well. I recommend leaving the PGP 8.1 CT alone. The filter choke needs to be pretty big, at least 15H, to get proper performance at full current, and at that inductance it needs to be rated for the full AC also, probably 100mA or more. The caps need to be rated for 1kV peak, of course (660 VAC). If you do it as cathode bias (69VDC) you drop to about 525VDC across the 845. The operating point is very good - it only dissipates 32W ( those $40 a piece Chinese 845s will last forever! - B.) and you’ll get 7.5W output. Pushing driver plate voltage down to 200VDC and running it at 4 mA, you will get into 10K Rp territory, 12AT7 types could work.” Doc drew up a rough and ready schematic, which is shown on the next couple of pages. This is an untried circuit, but as usual we have a pretty high confidence level in it’s performance. What we would like to do is invite your questions and commentary on the Bottlehead Forum of Audio Asylum. We will use the Forum to offer up refinements on parts values and info on things like the availability of that unamed MagneQuest filter choke... EXO-50 parallel feed output transformer 5K primary, 16,8,4, ohm secondary, 20 watts, M6 and Permalloy “Pinstripe”, $550 the pair EXO-04 plate loading choke 50H, 60 mA, 317 ohms DCR, $198 the pair BCP-16GC grid choke!!!!!H, no DC, $80 the pair PGP 8.1 power transformer $165 the pair C4S active load kits $35 the pair Large Richard a Parafeed 845 Se amp Power SupplySchematic 10VAC filament transformer could be Mouser PN 553-VPP105600 (Magnetek10VAC 5.6A) Filter caps could be Mouser PN 5987-660V30 30 mF 660VAC C-D motor start cap 15H 75mA choke from MagneQuest TBA Use double UF4007 to handle voltage peak See Buddha article in this issue for info on reverse recovery spike filter ahead of full wave bridge Large Richard a Parafeed 845 Se amp Amplifier Schematic Try Mouser PN 5987-660V2.0 C-D motor run cap for parafeed coupling cap, or other 2-3 mfd 1kVDC rated cap. MagneQuest BCP-14 with 100Kohm 5W wirewound resistor may be substitued for C4S load and 62K WW resistor. Don’t leave out the 100mfd cap! 50 ohm 10Watt pot may be available from All Electronics, www.allcorp.com, PN POT-50C Use your favorite flavor of wirewound resistors. Ohmites are very alright in Doc’s book. da’ basics Basic design considerations for plate loaded triode stages Here’s an very cool reparte that occurred between Bart Shepard and Paul Joppa, after Bart requested some enlightenment on the Sound Practices “Joelist”. Note here that Bart is very humble in his asking for help, but that he has obviously studied hard to figure which questions to ask - he’s not just throwing cookbook circuits together, but rather he’s working to grasp the knowledge tht will let him design his own fantasies - dass’ what I’m talkin’ about!!! - B. Hi guys, I have a couple of really basic design questions that keep bugging me and thought I’d ask them here to see if any of the very knowledgeable guys on the list could sort me out. I am interested in the design of a basic plate loaded triode stage. As I understand it a constant current through the tube will provide for minimum distortion and maximum gain. Hence all the fancy totem poles and CC sinks and sources around. — yes; though power supply isolation is another benefit. I also understand that these effectively provide a very high impedance load. — yes some 60dB isolation. That’s why John Camille pushes for those high impedances. I know several people who claim to hear the difference; my own direct experience is not enough to make any claims. Does the noise of the load R become a problem? If so, in what circumstances? Is this just an issue for pre-amp stages? Surely not for high voltage swing driver stages. — yes, it does. Most bulk resistor materials (carbon, sputtered metal) exhibit some noise voltage proportional to the voltage across the resistor, in addition to the thermal noise common to all resistors. The higher the voltage, the higher the noise; consequently it cannot be ignored in driver circuits. Solid metal resistors (wirewound, bulk foil) show much less of this behavior. That’s why Mills wirewound are typically called for as plate loads. Also the voltage capability of the resistor is a limit. Most resistors are rated for 200v or so. So a “good” plate load might require several resistors in series, if operating from a 1000v power supply. The next limitation I am aware of is the resulting high Zout for the stage. This leads to my next question. — the output impedance is the plate resistance in parallel with the load resistance; it doesn’t go up more than 30% or so relative to a conventional resistor-loaded circuit. Often the CS loads are used with an unbypassed cathode resistor, however, which raises the effective plate resistance by (nearly) mu. That can be a problem. My first question is what limits just using a very large plate load resistor? The usual limitation quoted is the high B+ voltage required to provide the desired plate voltage. But in , for example, a 211 or 845 power amp, high B+ is not a problem. How do I calculate the maximum Zout allowable to correctly drive the output load (e.g. should Zout be < 10% following stage Zin??) and in fact how do I calculate what this load is when it is the grid of a following stage? — depends on how high an impedance you want. Just looking at the plate curves and thinking of distortion, a load impedance of 2-3 times the tube’s Eb/Ib gets you most of the way. But for power supply isolation, that only buys you 10dB or so. Very high load impedances can be achieved - I think the CCCS is at least 10 megohms - that gives — Usually the most important factor is the grid capacitance. There are two limitations, frequency response and current capability. Frequency response is the driver source resistance (see above) interacting with the capacitance. Most designers seem to think that a -3dB frequency of 100kHz or more is desirable. For current capability, I think it was jc morrison who said that the stand- ing current in the driver stage should be 5 times the rms current drawn by the capacitance at 20kHz. Both of the above criteria seem to be quite conservative. If I design to not have to drive the following stage to extremes I should be able to avoid grid current, shouldn’t I? So shouldn’t this load be not much lower than the grid resistor for a self biased stage? — Only very few tubes have a max. grid resistor so low as to be important here. The type 50 is an example; it specifies a maximum 10k grid resistor as I recall. Do I need to take into account Miller effect as an additional load? If so, how? ( add Cgp & Cgc then times gain??) Should this reactance be > 10 times the load on the grid?? or does plate load only affect this re frequencyresponse? — Certainly; see above; it’s the dominant load usually. Strictly it’s Cgp times gain, plus Cgk, plus stray capacitance depending on layout. It’s usually good enough to use Cgp times mu. Does the nature of the following stage matter? It seems that output stages running high currents need better drive than low current VA stages. Why? — Basically, output tubes are physically large and have highter capacitances. Plus they need lots of drive voltage, which increases the current into their capacitance, thus increasing the minimum standing current in the driver. Is this due to a need to be able to supply drive current? If so, why, if not driving into grid current or does grid current start at biases well above zero volts?? — as noted above, it’s the drive current into the grid capacitance. There probably is some advantage to being able to drive into class A2 on transient peaks, but that’s a whole different can of worms. (Incidentally, *some* grid current shows up when the grid is within 2V of the cathode, depending on details of the materials...) Or is it due to a need provide a low impedance load on the grid for some rea- son???? — no Is a low driver Zout only required for its ability to deliver drive current or are there other reasons? — As above, the frequency response is another consideration. What appear to be trivial basic questions soon seem to get pretty involved to me and I haven’t found the real answers easy to come by in any of the introductory texts I have looked it. A lot of this stuff seems to be skimmed over, an infinite grid impedance not requiring any current!! — yes. Sorry if this stuff is real basic but perhaps there are others like me who get OK results but don’t really deeply understand the issues and your responses may help them also. Cheers, Bart ( not too proud to ask :-)) Entwined interconnect cable kits from Electronic Tonalities pre-cut twisted pair 20.5 guage High purity continuous cast long crystal solid copper conductors with a high temperature insulative coating, pre-cut polyethylene outer jacket and Vampire Wire RCA plugs $39 .5 per meter pair, $49 per 1 meter pair, $59 per 2 meter pair VALVE the magazine of astounding sound THE PENTODE ISSUE A Novel Tranformer-Coupled 6V6 Stereo Amp A Doc B. Modded Zen 84B Twelve Ways to Parafeed What I Wished I Would Have Known About Dual Volume Controls... Heavy Metal and more... volume 6 number 5 1999 “If it’s musical refinement you’re after, this is the address you’ll be looking up.” Peter Breuninger, Listener, Autumn 1999 “...the Paraglows are very good music-makers: insightful and immediate, with excellent pacing and pitch accuracy. They drive Lowthers beautifully well— ditto Galantes...” Art Dudley, Listener, Autumn 1999 “In one word, GLORIOUS!!! … After only a few hours of break-in, they presented a soundstage from room edge to edge, with at least five feet more of depth than I’ve heard before. Even on digital, I could make out hall sounds never heard before...The mid range was almost palpable, with voices taking on that three dimensional quality of a living body. Bass down to 50 Hz. was tight, controlled and THERE. Measurement showed it to be flat down to at least 10 Hz ... Highs extended out as far as I could hear.” Bill Gaw, EnjoytheMusic.com, November 1999 Paraglow— Currently inhabiting the listening rooms of Lowther America, Avantgarde Acoustics, MagneQuest and Listener Magazine. www.bottlehead.com VALVE the magazine of astounding sound Chief Editor and Publisher Dan “Dr. Bottlehead” Schmalle Managing Editor Brad “Just fell off the turnip truck” Brooks Chief Administrator “Queen Eileen” Schmalle Resident Smart Guy and Technical Editor Paul “Braniac” Joppa Resident Hot Iron and Dr. B’s Bodyguard John “Smoothplate” Tucker Big gun OEM advisor Michael “Airgap” LaFevre Contributing Editors David “Full Track” Dintenfass “Crazy Eric” Lenius VALVE P.O. Box 2786 Poulsbo, WA 98370 by phone: 360-697-1936 business hours: 9-4:30 PST, Mon -Fri technical queries: Thurs. 12-4:30 PST fax: 360-697-3348 e-mail - [email protected] Editorial and Advertising Inquiry 1428 Roberts Ave. Nashville, TN 37206 by Email: [email protected] by Phone: 615-228-2792, evenings CST Let it ring... VALVE in no way assumes responsibility for anyone harming themselves through exposure to the contents of this magazine. We believe electrons flow from minus to plus, and that they can kill you along the way if you’re not careful. Vacuum tube audio equipment operates at potentially lethal voltages. Always treat it with respect. Many ideas published in this magazine are untried, and involve the use of potentially dangerous parts and tools. In attempting any idea or project published herein, you assume total responsibility for your actions and any harm caused to yourself or others. This publication is produced as a service to the audio community and is wholly owned and published by Electronic Tonalities. The intent of this publication is to offer ideas to inspire and educate audiophiles in an effort to increase their understanding of the audio equipment that they use and cherish. Blatant copying of the circuits published in this magazine for use in commercial products shows a complete lack of original thought. Don’t just copy and distribute stuff without the author’s and publisher’s consent, OK? editor’s thing Season’s Greetings! I am really excited by the opportunity to edit my favorite audio eXperimenter's and DIY magazine. Under Doc’s guidance, VALVE has developed into a valuable resource for audio eXperimenters and Hi-fi enthusiasts around the world. As the new editor, I am excited by the challenge of continuing to offer exciting technical features. VALVE will continue as a tube enthusiasts, experimenters and DIY journal, just like when it started back in 1994. It has been a formula for success since the beginning, so why change now? You can see for your self—the VALVE CD-ROM Archives are now available. Was VALVE ahead of it’s time? Maybe. I think that it was innovative even in it’s humble beginnings as a simple club newsletter— get the back issues and check it out. Look forward to a few small changes. Beginning January we will be publishing VALVE quarterly. We will also be revamping the VALVE web page, and we will be posting additional goodies there in-between issues. I will be eXperimenting with various formats to enable you to use this document easier. PDF format is great, and we will continue to distribute VALVE in PDF format. I will be looking at ways to make it work even better as a screen document, so it is easier to read at work (on breaks only!) Do not have your BAN up and running yet (Bathroom Area Network)? So print it out. That way you can read it on the bus, or while waiting in the car at the mall while your “dear heart” shops. Either on screen, or as a printed document, your choice. We will constantly be tweaking. We will be searching out more advertisers of DIY kits and parts to include in VALVE. Our ad costs are reasonable, heck, they are dirt cheap! Look forward to new sponsors in the coming issues. Thanks to everyone for your patience while we produced this latest issue. Please drop me a line now and again with feedback on how we are doing. Thanks to Dan, Eileen, Paul, Dave, John T., John C., Mikey, Eric, and all others who have contributed thus far to make VALVE what it is. They have set the bar high. I thank Dan for the opportunity to continue his fine work. Happy New Year everyone, and Don’t let the blue smoke out! Without further adieu, we bring you: THE PENTODE ISSUE On the cover: Cameron Etezadi’s 6V6 amplifier. Read more about how he designed and constructed this screamin’ blue amp and power supply. Keep those equipment Glam shots coming! new classics from First Impression Music FIM XRCD 022, The Artistry of Linda Rosenthal Linda Rosenthal, violin, Lisa Bergman, piano A collection of timeless violin solo favorites, by the most talented student of Jascha Heifetz with dazzling skill, dynamics and colors. You have to listen to believe. A must for demo. FIM XRCD 2000, Messiah by George Frideric Handel Yvonne Kenny, Paul Esswood, Martin Hill, Magnus Linden Members of the SWEDISH RADIO SYMPHONY ORCHESTRA THE STOCKHOLM BACH CHOIR ANDERS OHRWALL. Conductor Recorded live at the Adolf Fredriks Church in Stockholm, Sweden, on February 13 & 14, 1982 #189 16149 Redmond Way Redmond, WA 98052 http://www.fimpression.com Tel: 425-868-5326 Fax: 425-836-9061 A NOVEL TRANSFORMER-COUPLED 6V6 STEREO AMPLIFIER by Cameron Etezadi ABSTRACT Certain types of music or certain types of speakers require more power to drive them to acceptable volume levels than a relatively inexpensive DHT or other SE configuration can produce. The inexpensive solution to this issue is construction of a push-pull amplifier, with the resultant change in sonic character such a topology brings. This article details the construction of an inexpensive and effective push-pull amplifier, offering excellent sound at increased power levels. Some interesting design tricks are employed; these may be successfully utilized in other single ended or push-pull designs. The result is an amplifier with an almost flat frequency response from approximately 18 Hz all the way to 24 kHz, 0.58% THD at 1 W, and no shortage of detail or bass, yet with a total finished cost of less than $600, well within the budget of the average do-it-yourself builder. INTRODUCTION When the Whammodyne! speakers were first published in VALVE, a copy quickly became my main reference pair of speakers. They offer remarkable efficiency, extreme detail, and have a reasonable frequency response. These speakers were bi-amplified with identical pairs of homemade 6GW8/ECL86 single ended amplifiers, using parts scavenged from old phonograph amplifiers generously provided by both my mother and George Wright. This setup worked well for a while, but the strained three watts per channel provided just could not handle the heavier passages of more modern, contemporary music, nor could the meager power supplies and output transformers keep up with the dynamics of the more refined classical or jazz pieces. Given these shortcomings and a slim budget to spend on audio equipment, the design of a cheap, yet reliable and high fidelity push-pull amplifier was sought that could remedy this situation. The limitations and drawbacks of push-pull designs are obvious, yet the more reasonable prices of the output transformers, coupled with the higher power levels available from such configurations make it the logical choice, if the price to performance point for this project was to have been reached. DESIGN CRITERIA AND GOALS This amplifier had only two major goals; these seem to be the common goals of all VALVE projects: good sound and a price as low as possible. With these two goals in mind, the search began for parts to use. One of the easiest ways to bring the price of any project under control is to scrounge. The Puyallup, Washington hamfest was a great help here; for those in the eastern part of the country, a spring trip to the Dayton Hamvention would be in order every year. A suitable old TV transformer and a heavy duty military surplus choke inductor of 5H at 300 mA were found, each for $5. Several chassis were either bartered for or purchased on the surplus market for under $10 each. Inexpensive NOS tubes were also procured for $1 each or less. Once the junk box was reasonably stocked, the amplifier layout could begin. First, to keep cost at a minimum, two power supplies would be impossible. Each would require a chassis, a large heavy transformer, and a matching choke. Finding more than one transformer of a matching pair was not possible. That meant the stereo supply had to be shared between the two audio channels. Monoblock amplifiers provide better sound quality, though, as the two audio channels do not couple to each other through the power supply. To ensure adequate decoupling in the single supply, the power supply for this amplifier is regulated, with each channel being routed through a separate series pass element and utilizing an independent voltage error amplifier. Adding additional regulator parts is cheaper than adding another transformer and choke, unless one happens to have a matched set of two in his junk box. Furthermore, there are additional benefits in a regulated supply, specifically in the area of supply impedance, which make it worth considering. A regulated supply will also help remove a few extra decibels of hum from the circuit, leaving more headroom for the music. Hum was a major problem in the supplies of the 6GW8 amplifiers, and great pains were taken to eliminate it from this amplifier. The only downside to a regulated supply is a lack of the sonic effects of “tube rectifier sag” upon the circuit. This effect is often desirable, and many of the projects presented in VALVE are often the subject of rectifier swap tweaks to change their sonic signature. However, the intent of the project is to hear the amplifier, and not to listen to the power supply for the circuit. Scavenging my inventory for suitable tubes to use in this project, valves were chosen that were either in current production, large surplus supply, or easily replaced with solid state components, should the need arise. Also, the search was limited to the use of octal based tubes, exclusively. Most of the pentodes and tetrodes and beam power tubes that are suitable for audio output are based in an octal fashion. Excellent preamplifier tubes are also available in this size. Keeping the size uniform throughout the project permits a single size of socket, a single size set of hardware, and a single hole saw to bore the chassis out, thus saving several dollars overall. The 6V6 tube was picked for audio output. This tube was common in early guitar amplifiers, but was largely replaced with the larger 6L6, EL34, or 6550. Few guitar amplifiers past the late 50’s or early 60’s were designed with this tube. It retained some popularity in hi-fi circuits, but almost always ended up playing second fiddle to larger, more powerful tetrodes and beam power tubes. The 6V6 is rated for more than 14 watts in push-pull, fixed bias operation, which is more than enough to drive the Whammodynes!, and should certainly suffice for the much less efficient speaker projects that are planned. For output, the first choice was to try a pair of Brooklyn B-15 transformers, which looked like a good, cheap way of getting the sound from the tubes to the speakers. The circuit needed an ultralinear output configuration to reduce the distortion in the amplfier and to simplify the output tube hookup. After some consultation, MagneQuest would not build the B-15 with ultralinear taps. Instead, one of the first production pairs of MagneQuest MQ-565 output transformers was obtained. They are at about the same cost and offer great performance for not a whole lot of money. Ease of use of the amplifier was also important, so a cathode-bias arrangement for the 6V6 tubes is employed. Re-biasing the tubes with each tube swap was not an appealing thought. Also, fixed bias causes even more complexity in the power supply, as a bias supply must then be derived. In the driver for a push-pull amplifier, some method of phase inversion must take place, as the signals applied to the grids of the output tubes must be 180 degrees out of phase. Various schemes for phase inversion have been developed, both active and passive. The active methods all suffer from a voltage gain of less than unity, since they employ some form of cathode follower output, unless an additional gain stage is employed. That additional gain stage is usually an RC coupled amplifier, although it may be direct coupled. The major disadvantage of this arrangement is the need to balance the phase inverter carefully. Another possibility exists for doing the same task – a transformer coupled stage. Antique Electronic Supply makes a PT-157 nickel core interstage transformer specifically for driving push-pull grids from single ended output stages. Transformers are remarkably easy to use and need no balancing. The tradeoff is limited bandwidth, as well as saturation of the nickel core if it is overloaded with DC current. The bandwidth limit cannot be circumvented, but the DC saturation can be prevented by not placing any DC on the primary leads of the transformer. Thinking back to basic electronics, just about any inductance can be replaced with an active load. Most octal triodes are dual triode units, and hence provide can have one triode used as an active element for loading the lower, voltage amplifier stage properly. Here, a mu-follower configuration provides the proper loading for the 6SN7 tube chosen to be the voltage amplifier. The output of this stage is then transformer coupled (with a DC blocking capacitor in series with the primary lead of the interstage) to the grids of the second stage. The PT-157 has been explored previously in VALVE articles. It is a cheap part (at under $13 each) yet sounds surprisingly good. Placing it on an oscilloscope and subjecting it to a square wave, however, is a little bit disappointing – there is a lot of overshoot on the rising edge of the peak, and the frequency response is very clearly frequency limited, even in the audio range. However, it can be significantly improved by loading the output down with resistors. Subjectively, the transformer sounds great and the nickel core is really fast when listening to complex passages. With the cost coupled with reasonable performance, at least subjectively, this part looked like an ideal choice. Now that the amplifiers’ tubes were selected, and a rough idea of operating points located, the design of the power supply could be completed. Given the heavy choke, large power transformer, and the complexity of the additional regulation circuitry, the power supply was built on its own separate chassis. This arrangement permits later substitution of either amplifiers or power supplies, should the need arise. It also allows further physical separation of all the units to reduce magnetic coupling between transformers wherever possible. Lastly, it allows a much smaller chassis for the whole unit, which means already owned chassis units could be used. For the heater supply, there were two choices – AC or DC. DC won out easily. In an amplifier like this one, there is hardly a good reason not to use a DC supply here. The parts count is small and it squeezes a few extra decibels of hum out of the amplifier. It provides a low voltage to drive any solid state components on outboard amplifiers, and is so easy to provide with the three terminal regulators that are available. Here, the circuit uses the LM338, which is a five amp, three terminal adjustable regulator, to provide this voltage. With a large 10 gauge steel chassis, heat sinking this part was not an difficult task. For the B+ power supply, the circuit was originally designed using the high gain 6SL7 dual triode in a cascode configuration as an error amplifier for each half of the 6080 series pass regulator tube (a 6AS7G would also work here.) The reference voltage was supplied from a 0D3/VR150. It could just as easily have come from a zener or string of zeners, but the beautiful purple glow of a VR tube is not to be missed. Zeners are also noisy, but they do yield a much more stable reference voltage than a gas tube. However, after building a copy of this circuit, the cascode error amplifier could not be stabilized enough to keep the circuit from self-oscillation when the output voltage was lowered to an operating point usable with the 6V6 tubes. As a result, the circuit was switched to a variant of the regulated power supply available in the “GE Essential Characteristics” book (see references at the end.) The gist of that circuit is almost identical to the one previously used, except that the relatively complex cascode error amplifiers are replaced with much simpler pentode based (6SJ7) ones. Working the numbers through, after the fact, for the old and new circuits revealed operating points that were “impossible” for the old circuit and flawless, safe operating points in the new. Power supply design, even in the case of a regulated linear supply, can be tricky, and unlike much audio design, where trial and error based on reasonable assumptions will often work, there is simply no escape from pushing the pencil across the page. Lastly, the HV supply rectification is done by high voltage, high current silicon diodes. With a regulator in the circuit, one is simply not going to hear a sonic signature of a vacuum regulator. Save a couple of dollars and the space on the chassis and go with solid state. Increased reliability and lifespan of the solid state components, plus a lower voltage drop across the rectifier comes as a bonus. A well designed regulator does not permit the voltage to vary much from the designed value; it also serves to control much of the ripple. Ergo, the surplus voltage afforded by the solid state diodes is useful in providing overhead for the regulation drop. The variance in output voltage as a function of current, or “sag” that is inherent in a tube regulator, would be masked by the series pass element and error amplifier, unless this circuit was malfunctioning. In fact, load regulation in this supply is on the order of 3VDC over the design range of output current, and ripple should be less than 5mV, if good construction practice is followed. For smoothing prior to the regulator, an LC filter configuration provides a peak DC of 90% of the transformer’s AC voltage; a CLC configuration would yield a peak of 140%, instead. The regulator will make up for the slightly lower ripple reduction from the filter with one less half-section. THE POWER SUPPLY CIRCUIT Figure 1 shows the power supply unit. The important bits of this circuit will be discussed by subcomponent. The circuit itself was built with point to point wiring for the HV supply and on perfboard for the heater supply. Scraps of perfboard were used for the voltage divisor network on the HV supply feedback loop, however, to facilitate mounting of small PCB-style ½ W trimmers. Figure 1 – Dual channel regulated B+ supply, 200V – 400V @ 125 mA/channel, with single 6.3 VDC @ 5A heater supply The simplest and easiest part to start with is the DC heater supply section, which is in the upper left hand corner of the diagram. The DC heater supply is filtered and regulated. The LM338 is a three terminal adjustable regulator housed in a TO-3 package. The third terminal is the case itself, and it is the “adjust out” line, so mounting this part must isolate its body from the chassis. Mica washers and TO-3 mounting kits are fine, but be sure to heat sink everything well and use silicone grease. The part is capable of five amps of current, but will generate quite a bit of heat. Forced air is not necessary, but stuffing this part inside the chassis would be a bad idea. This is also not a low-dropout regulator, so if you have the five volt winding on the transformer, or can squeeze more than the requisite 6.3 VAC out of a filament winding, it will appreciate the extra overhead. It is a linear regulator, however, so this will burn off as heat. The extra capacitor across the adjustment potentiometer serves to reduce ripple, and is not required, but given the price-for-performance improvement for a 15 cent item, include it. The two additional diodes (1N4001 or something similar) serve to protect the regulator from the discharge path of the hefty (1000 microfarad) capacitor on the output filter side and the much smaller ripple-reducer capacitor. The 0.01 microfarad ceramic capacitors are a design habit. They may be left out if so desired. There is no proof that they make a difference one way or the other, but my drawer is full of them, so they get used a lot as extra bypass capacitors. By not using these parts, there is a risk of blowing out the regulator under certain power-down scenarios. The regulator is not a cheap part (about $10) and sometimes hard to come by. A simple CRC filter could be used, instead, but would be a bit noisier than the regulated supply here, yet would still offer a major improvement from AC heaters. On the high voltage side of the supply, there are a couple of interesting pieces. Most of this circuit comes almost directly from the General Electric Essential Characteristics guide, which most tube enthusiasts should have as part of their reference library. The input to the power transformer has a thermistor current limiting device in series with the primary of the power transformer. This part is available from Mouser and is 10 ohms cold, 0.1 ohms hot. It will limit the inrush current nicely, and prevent turn-on surges. A major problem with the initial power supply design was blowing fuses prior to insertion of this part. Part of that problem stemmed from the initial CLC filter design, which basically presents a dead short to ground for the first half-cycle of the AC waveform, until some charge has built up. Needless to say, some sort of current limiting is good here. Note that the audio tubes will never have high voltage applied before they have warmed up, because the output voltage is dependant on the regulator’s conduction, and the 6080 is a slow tube to warm up. Also, the LM338 has current foldback, so input surges are limited to the heaters of the audio power supply automatically, regardless of whether the thermistor is there or not. On the secondary side of the power transformer, there are small resistors in series with the rectifier diodes. These help to quiet the spikes in the transformer. Before inserting them on a hint from George Wright, the power supply diodes would routinely fail in a catastrophic and often spectacular manner. The transformer in this project was designed for an old tube television set, and as such, is more of a match for a tube rectifier. Solid state rectification really needs these resistors to be happy. The regulator feedback mechanism is pretty self-explanatory. Matching resistors or tight tolerance items are unnecessary, although use metal film resistors wherever possible in power circuits. They retain their value over time, unlike carbon composition resistors, and are thus better suited to the strain and demand of power supplies. Remember, also, to watch the voltage breakdown ratings of whatever resistors used in the project, as the raw voltage in this supply is around 400 volts, more than many resistors can handle. There absolutely must be a separate filament supply for the power supply tubes. This supply has to be floated above ground; failure to do this simple action will exceed the cathode-heater breakdown voltages for many of the tubes in this supply, and will lead to undesirable quantities of smoke being emitted from the device. Two 1K resistors, as shown, coupled to the 150V reference source provided by the VR tube will more than suffice. In addition, a small capacitor across the VR tube will shunt some of the highfrequency noise inherent in these tubes to ground. Keep it less than 0.1 microfarad, or this type of tube is prone to oscillation. The output capacitors on the power supply (after the cathodes of the 6080, in the lower right portion of the schematic) are simply electrolytics, of about 10 or 20 microfarads at 450V. Use a much higher rating here than the supply is worth, as the supply voltage is variable, and component tolerances, settings, and errors in the first pass at building this supply may result in voltage higher than a “marginal” 350V capacitor could handle safely. Also, the cost difference is almost insignificant between the two. It is a small price for a little safety. Do not waste expensive polypropylene capacitors prior to the regulator – an audible difference will not be heard. The meters in this project are surplus, PM-89 style, and are easily obtained from Antique Electronic Supply or from All Electronics Corporation. They are wildly inaccurate, but give a nice ballpark reading to ensure everything is healthy. An AC ammeter would also be nice on the input side of the transformer, and might be a nice replacement for the DC one. The DC ammeter reads >1A all the time, which, according to a Fluke multimeter, is off by a factor of ten! The voltmeter is within about 10% of the actual value. Higher quality meters would be a nice investment, or that part of the circuit could be left out all together, as it is essentially set-and-forget. The meters mostly serve to point out the tube age in the power supply. As the 6080 ages, it will likely cause the output voltage to drop, and that should signal replacement. Do not use these meters for actual adjustment of working voltages – set those with a high quality DMM. On the voltmeter – 400VDC units are difficult to come by. Here a 100VDC unit is employed and the faceplate remarked by scanning and editing it, then cutting out a highquality laser printout, and pasting it on with 3M spray adhesive. If the voltage divider is used to provide a sample voltage for this meter, it becomes more critical to match the 47k voltage divider resistors to avoid introducing more inaccuracies in the measurement; close matching will keep the errors to a minimum. Use high quality resistors if any accuracy is to be expected. On layout, be careful to space the 6080 (or 6AS7G) well away from other components in an area of the chassis where good air circulation can be obtained. This tube gets quite warm and needs to remain relatively cool. All the output voltages and grounds are run to Jones style jacks on the rear panel. Use six-pin jacks, wired with the center two pins as ground, and ensure that, while the plugs are polarized, excessive force in inserting them the wrong way would not produce high voltage on the heater line, nor the converse. This actually makes it reasonably safe to plug and unplug these items while “live”; at the least, it is not much more hazardous than standard mains plugs on the wall. Figure 2 - Jones socket wiring (top view) The power input jack to this unit is a standard three-prong unit (IEC), but features an inline RFI/EMI suppressor. These units are available surplus for as little as $1.50, and are a worthwhile upgrade for any and all equipment featuring this style of connector. THE AUDIO AMPLIFIER CIRCUIT The audio amplifier circuit is fairly straightforward for a transformer-coupled amplifier. The schematic appears on the next page (figure 3). Figure 3 -Transformer coupled audio amplifier Each amplifier connects through a private “umbilical” cord terminated in a six-pin Jones plug that mates with the jacks on the main unit. Each Jones plug is wired identically, as illustrated in figure 2, so that the side of the power supply used is irrelevant. The jacks on the power supply only bring out one B+ channel to each socket, and it is a different one between left and right sides. The umbilical cords feature snap-on ferrite core chokes obtained from All Electronics Corporation, as an added reduction measure against any high frequency noise that might have been introduced in the cable run. The cable itself is also shielded four-conductor Belden wire, with the shield grounded only to the power supply chassis ground bus. Note that the heater supply is completely isolated from the ground of this unit. This reduces hum; the filament supply is referenced to ground in the power supply -connecting it here to the chassis would only cause a ground loop. This setup also allows the use of an AC heater, should a low cost power supply be built, instead. However, the “on” lamp, a blue LED, is fragile, and should be either eliminated or diode-protected (another 1N4001 in series would do) in this case. Note, too, that substituting another color of LED for the blue would require changing the dropping resistor value, as blue LEDs have extremely high voltage drops across them. As far as the audio circuit is concerned, the number one noise elimination step to be taken is the utilization of a star ground in the construction of this unit. This technique should be a standard construction practice, anyway. Pick a good, centrally located point and solder the ground to the chassis, if it is possible. If the chassis is aluminum, use the mounting screws of the terminal strips to make the connection. Starting at the output end of the amplifier, the tubes’ operating point is set by the cathode bias resistor. Here, it is a 280 ohm cement unit. The operating point that should be aimed for is approximately –20V of grid bias at 315VDC B+. The 280 ohm cement resistor has to supply the current for both output tubes. The maximum output current is about 100mA, combined, at peak AF input voltage (for the pair of tubes). This gives a grid bias of about –28 volts, a bit high. However, normal drive on these tubes uses much less current, and the more reasonable zero-signal usage of 70mA across two tubes combined leads to about –20 volts on the grids. This value is not terribly critical, and is worth experimenting with. Note that a very large bypass capacitor could be used here – on the order of 4700 microfarads at the appropriate voltage. This value would serve to maintain that 20 volt bias during high power transients. A large value is necessary to prevent the time constant of the cathode resistor-capacitor circuit from delaying the transient response. Individual resistors, which would be a good upgrade and reduce the need for a matched pair of tubes, would be of a much higher value and could benefit from bypassing by smaller electrolytics. If the cathode resistors are split, these capacitors become necessary to prevent the introduction of negative current feedback, which would reduce output impedance and increase drive requirements. Alternatively, connect the two cathodes together with a non-polar electrolytic. The 27K resistors on the secondary of the interstage coupling transformer serve to load the secondary down, as well as to load the grids of the 6V6 tubes. These resistors improve the sound of this transformer as well as its frequency response. The most complex part of this entire amplifier is the input stage. S.E.X. amp kit builders might recognize the mu-follower configuration used here. In the case of this amplifier, not only does give increased linearity of the lower stage from the active loading of the upper stage, but the nickel core interstage now no longer needs to carry DC, as it would if it were to provide the load for the plate. Honestly, the nickel interstage simply lacks the impedance to be used well as a direct load of a voltage gain stage. The following bit of theory, paraphrased from Paul Joppa, allows effective design the input stage: Good operating points for this configuration have Eb/Ib = 4 * rp or potentially more. Since the interstage transformer’s impedance is fairly low, this should be kept fairly low. rp for a 6SN7 is about 7700 ohms, so an operating point of about 150V at 5mA, per triode section is about right. Remember that they are stacked one above the other, for a total drop of about 300 volts. With cathode bias, one figures that: 0.7 * Eb / mu should provide the bias voltage. Mu is 20 for this tube, so, plugging in from above yields 5.25V of bias. With ohm’s law, that gives the cathode resistors as: R = E/I = 5.25V / 0.005A or 1050 ohms. 1.1K is a standard value that is close enough in a 5% tolerance. For a mu-follower, figure on about a 20% drop at Eb across the current sensing resistor. So, the plate resistor for the lower tube, which is really the current sensing resistor, should have, from ohm’s law again, a value of: (0.2)(150V) / (0.005A) or 6000 ohms. 6.2K is again a close enough standard value to use here without worrying. An arbitrarily picked value of 470K provides a nice grid resistance. It is possible to go as high as 1M here, but consider the input impedance of the amplifier when choosing this value. The grid coupling capacitor should then be chosen based on this value. Paul’s formula lists 30000/R, where R is 470K, or about 0.06 microfarads here. Just use 0.05, which is close enough. The input capacitor was initially the same, although it was later replaced it with a much nicer Solen 2.2 microfarad unit left over from the Whammodyne! construction. Lastly, the DC blocking, or coupling capacitor should be as large as possible to allow the bass to really play though. At a bare minimum, it should have enough reactance to match the transformer inductance at the load impedance, which, for the transformer used, is about 6 kohms, as shown with the load. This translates into about 30H, or 6 kohms at 32Hz. So, the coupling capacitor should be: C = 1 / (2 * pi * f * X) where f is the frequency and X is the reactance. Using the supplied numbers, this works out to 0.82 microfarads. 1 microfarad should be fine, and, finding a great surplus deal on 1 microfarad, 1 kilovolt polypropylene units, this was exactly what went into the amplifier. Note that this value must be rated for the full power supply voltage, at least, just to be safe. PERFORMANCE DATA The most important characteristic of any amplifier naturally is how it sounds. Before heading into the subjective listening tests and commentary, here is some real performance data on the frequency response and the spectral output of this amplifier. Measurements were obtained through a HP 35665A Dynamic Signal Analyzer, courtesy of Dave Dintenfass. IInput (V) Output (V) THD % 2nd harm (dB) 3rd harm (dB) 4th harm (dB)5th harm (dB)Pwr out (W) 0.1 0.22 0.283 0.5 1 1.3 2.83 3.6 5.9 9 0.17% 0.58% 1.07% 4.38% 14.80% -58.4 -57 -52 -50.7 -35.8 -59.5 -45 -39.6 -27.2 -16.9 -71.3 -72.5 -67.6 -56.3 0.21125 -72.4 1.0011125 -66.8 1.62 -58.9 4.35125 -37.2 10.125 Table 1 – Performance data, 1kHz sine wave input, 8 ohm resistive load Table 1, above, presents the data that was taken in regards to the harmonics and distortion of the amplifier. Performance is excellent at low power levels, but degrades somewhat at higher levels. However, performance is still acceptable for the normal listening range. Here are three possible tweaks to lower the THD at higher power levels. First, the cathode bias resistor of the 6V6 should be lowered slightly, to raise the grid voltage, relative to zero volts (bring it from a full-signal –29V to closer to that magical –19V.) Second, this test used NOS Ken-Rad tubes. There was only one pair of Ken-Rads (the other channel sports RCAs), and they are not matched. Close AC and DC matching, especially in this common cathode resistor case, will improve performance somewhat. Lastly, at high power levels, the circuit may exceed what the tiny nickel interstage can handle. A heftier transformer here would drive up cost, but improve fidelity quite a bit. On the other hand, Whammodynes!, with just one good watt of power, perform fantastically, as long as the transients are handled gracefully. The recovery of cathode bias certainly affords that luxury. The harmonic data is certainly more telling in graphic form, and Figures 4 and 5 illustrate clearly the relative dominance of the odd order harmonics, as is characteristic of a push-pull amplifier. Note, however, that the even order harmonics are not particularly heavily suppressed – a result that is surprising, unless one refers to my earlier comment about not matching the tubes well. A nonbalanced match actually benefits in this situation, as the even order harmonics are quite pleasing musically. Figure 4 - 1 Watt Spectral Output, 1kHz Sine Input In the ten watt version, above, it is clear that the amp is beginning to distort, and the numeric data shows clearly that the third harmonic is only about 17dB down from the fundamental. Frequency response is excellent for this amplifier, which is a tribute to the output transformers used. The frequency response of these transformers is actually given by the manufacturer at full rated power, not the low power levels that may other companies use. As a result, the graph of frequency response is identical for all the power levels tried. Just one plot which is representative is included. Figure 5 - 10 Watt Spectral Output, 1kHz Sine Input Figure 6, below, shows the transformer’s –3dB points are 17.8 Hz, as well as 25.0 kHz, more than adequate for all listening, and certainly more than adequate for Whammodynes! (good, unfortunately, only to about 30 Hz). Figure 6 - Frequency sweep, 2 Watts output power The scale of Figure 5 is 1 dB per vertical division, so the spike at 30 Hz is not as dramatic as it appears on the graph – only about 2 dB above baseline, and it is centered exactly at 30 Hz. The –1dB points for this amplifier occur at 20.1 Hz and 20.4 kHz, which are effectively the upper and lower edges of what is considered to be the full audible spectrum. Obviously, this statement is not the exact truth, but most speakers fall into this range, anyway. The damping factor for this amplifier is 0.38, which is a little lower than might be expected. This value could be increased with some negative feedback, or, alternatively, speakers that work well with low damping could be used instead. This low number is indicative that this amp functions more as a current source than a voltage source, and as a result, with the proper speakers, can have quite low loudspeaker distortion. SUBJECTIVE PERFORMANCE The amp itself has replaced a bi-amplified single-ended setup and is now the main listening reference. Construction on the unit finished in April, and it has been listened to extensively and burned it in for quite a few hours ever since. The system setup used is either a turntable (a mish-mash of homemade upgrades to a cheap table, always in progress) or a Marantz CD-67, feeding a Carver Silver One Reference Preamplifier (a prototype), into these amplifiers, and out to the SuperWhammodynes!. The system is fast, responsive, and does not lack the bass punch that push-pull configurations often seem to suffer from. Highs seem to be a little bit suppressed. At the last meeting, Dan agreed, noting that the signature of the regulator tube was evident in the audio, perhaps contributing to that sound and feeling. The amplifier was also tested as a subwoofer amplifier when paired up with a set of horns in the Electronic Tonalities workshop. It performed admirably, bringing out a nice, full bottom end and having plenty of power to spare driving the 96dB subwoofers against a 100dB+ horn system. In addition, it was auditioned alone through a two-driver + tweeter vented box, using MCM’s heavier 5-inch aluminum drivers and the Whammodyne! tweeter. The performance was similar to that of the Whammodynes! at home, it and really shone nicely. TIPS, TWEAKS, AND UPGRADES There are quite a few areas of this amplifier that could be upgraded or improved upon. For those building the setup, or inspired to build pieces of it (since its design is so modular), here are some suggestions: ! Upgrade the interstage transformer. This piece is likely the first and foremost limiting component in the entire amplifier signal chain, and more metal is almost surely equivalent to better sound and power handling. Wirewound adjustable ! Install separate cathode resistors for the finals. potentiometers might even be better, here. Bypass them with polypropylene or electrolytic capacitors if so desired. This eliminates the need for DC balanced tubes to be used as finals, although AC balancing may or may not be something to play with. ! Remove that input capacitor from the grid of the lower half of the mu-follower. One less component in the signal chain is always better. Be careful, though, to only use gear that is safe to couple this way. ! Adjust the connection of the primary of the interstage transformer. There are eight possible configurations for this transformer’s hookup. Each of the following has two locations in the circuit: o DC blocking capacitor may be as shown, or it may be placed at the “high” side of the transformer, prior to the audio signal passing through the core. o The “high” side of the transformer may be connected either to pin 3 of the 6SN7GTB, for cathode-follower, low-impedance drive, or to pin 5, for high-impedance drive. o The “low” side of the transformer may be returned either to the cathode of the lower half of the 6SN7GTB (pin 6, as shown), which provides a minimal amount of feedback to the circuit, or simply connected directly to ground. Each of these permutations will make a difference in the quality of the audio from this amplifier, and moving this part around is one of the most interesting experiments to undertake. ! Employ a global feedback loop from the output of the transformer to the cathode of the mu-follower. Either voltage or current feedback could be used to further reduce distortion, at the expense of changing the frequency response of the circuit. This change may or may not be advantageous, given that the low-power distortion of this amplifier is very low. ! Replace the 6SN7GTB tubes with 6SL7GT tubes. The operating parameters of these two tubes are different, but they will actually use the same component values to achieve good operating points. The 6SL7 will provide somewhat more gain than the 6SN7 used here, but the circuit should perform just as well. Again, it is a matter of individual listening preferences. The 6SN7 is usually preferred in listening tests, however. Miniature dual triode tubes could be used as well in the same configuration, provided the operating points are recalculated. ! Replace the hefty tube-regulated power supply with a solid state equivalent. There is little question that tubes look impressive glowing on the stereo rack. However, the reality is that the supply electronics could be shrunk to a much smaller package through the use of high-voltage Darlington pass transistors, opamp dc error amplifiers, and the like. The hefty choke might not even be necessary – a CRC filter and good solid state regulation should do just as well (is this heresy in VALVE?) (Nope. Ed) If there is interest, write to the e-mail address below, and discuss some solid-state, high-voltage supplies built and used. The look of the tubes, especially the 0B3/VR90, and the ease of visually checking that the regulator is operating right are both advantages of tube-regulated supplies. However, the size of the power supply is quite unwieldy, except as compared with some of Dan’s wild amplifiers. ! Replace the LM338 with a smaller regulator and a pass transistor. More parts, yet easier and cheaper replacement. One could even use a three terminal regulator and two forward diode drops in the ground lead to achieve about 6.3 VDC. LM7805 IC chips, even the five-amp versions, are significantly cheaper than the LM338 used here. ! Replace the meters’ voltage divider chain with a single resistor and a meter rated full voltage, if more accurate readings are desired. Ensure the resistor has a breakdown voltage rating capable of handling the power supply maximum output voltage. ! Polypropylene output capacitors on the output of the series pass elements of the power supply, as well as on the decoupling resistor in the amplifiers themselves would be a nice upgrade and may make a minor sonic difference. ! A triode-pentode switch could be installed in the amplifiers. Use a 100 ohm, five watt resistor between the plate and the screen if this option is installed. The sound should change quite nicely. A small, 0.01 microfarad capacitor between screen and ground could be installed here, as well. ACKNOWLEDGEMENTS Much deserved thanks and a show of appreciation go to Dave Dintenfass, Paul Joppa, George Wright, and Dan Schmalle for parts, theory, feedback, and analysis throughout the construction of this amplifier and power supply. Without their help, it would not have been possible. CONCLUSIONS This amplifier plays everything from classic jazz albums and great symphonic performances to modern alternative rock. With such a selection, it is hard to find an amplifier set up that can deliver in all cases, and it may make sense to keep several sets handy for different types of music. However, this particular 6V6 amplifier works amazingly well, and seems to be a very acceptable and pleasing compromise. As always, comments, [email protected]. questions, and suggestions may be delivered to REFERENCES My father was an electrical engineer and went to college in the late 50’s and early 60’s. Most of his engineering textbooks have been more than valuable in designing vacuum tube circuits. systems: The following books might prove useful to those designing similar Gottlieb, Irving M. Regulated Power Supplies.U 4th ed. New York: TAB Books, 1992. Horowitz, Paul, and Winfield Hill. The Art of Electronics. 2nd ed. Cambridge: University of Cambridge Press, 1989. Kempton, R. G., et al. Essential Characteristics. 10th ed. General Electric Co., 1963. Millman, Jacob. Vacuum Tube and Semiconductor Electronics. New York: McGraw Hill, 1958. RCA Receiving Tube Manual. Harrison: Radio Corporation of America, 1964. Seely, Samuel. Electron Tube Circuits. 2nd ed. York: McGraw Hill, 1958. Products by: Allen Bradley Alpha Core Alps Black Gate Caddock CAIG Labs Cardas DH Labs Elna Cerafine Golden Dragon Grayhill Hammond Holco Hovland MusiCaps Hubble Jensen Kimber KR Enterprise LCR Caps Lowther Mills MultiCap Neutrik Noble OCSL Ram Labs Roederstein Solen Sorbothane Sound Care Sovtek Svetlana Tesla Vampire WBT Western Electric Wima Yamamoto and many more... Tube Linestages Passive Linestages Phonostages Single-Ended Amps from 2.5W to 25W High Quality High Fidelity Kits and Assembled Products Largest Selection of Components and Accessories The Most Informative Catalog in the Business AC Line Filters Mods & Modules VISA MasterCard Visit Our New On-Line Store http://www.welbornelabs.com Celebrating 11 Years of Excellence 1988 - 1999 Our 1999 Catalog & Design Manual features loads of kits, parts, books, software, schematics, fun projects and the usual information. It’s just $10 U.S. and Canada, $18 International, refundable. Visa and Mastercard accepted. International orders are welcome. Welborne Labs P.O. Box 260198, Littleton, CO 80126 USA Phone: 303.470.6585 Fax: 303.791.5783 Brainiac's Today's Topic: Ugly Ears (don’t ask!) - nation stack of 1.875 by 1.5 by 0.625 an interstage transformer inch and mounting holes about 2.375 inches apart (when they’re not all bent This unit is available for $13.95 from to heck! … don’t ask). It weighs 8 oz. Antique Electronics, and is one of the on my kitchen scale. small class of cheap interstage units available. There are several in the $10 This particular unit was given to me by to $20 range, made for old radios usu- Reid Welch; it’s the same one that apally. Nothing fancy, but their small size pears in his Glass Audio article of sevmakes for low leakage inductance even eral years ago. I’ve since given it to Tim without interleaving and they can some- Lollar who is building an experimental times be used with decent results. They P-P 6B4G amplifier. Jerry Cottingham are usually designed for SE drive of has discovered that if you carefully repush-pull output tubes, but this one move the paper wrapping and expose offers either push-pull or single-ended the secondary wires, the center tap can drive. Generally they are not optimum be separated so that the two secondaries for single-ended output. In my experi- are accessible. This would permit sepaence these transformers are often very rate bias voltages in push-pull, for ininaccurate in their specifications; they stance. I have not tried this, so caveat should be measured before a circuit is emptor! designed around them. This one is attractive because it has very good high All the data below is for single-ended An occasional review of some nifty ...an occasional review of s frequency extension and will handle drive, ignoring the primary center tap. chunk of iron (usually cheap!) chunk of iron (usually chesubstantial DC current, though it is quite demanding in drive requirements. by byPaul PaulJoppa Joppa It is in a U-channel frame, with a lami- Heavy Metal Low frequency data: Turns ratio: Primary: Secondary: DC current: 1CT:1.5CT; specified for 7k CT:15.8k CT impedance 230+248 ohm DC 402+306 ohm DC Inductance with 12v/60Hz excitation is 7.9H at 0 mA, falling to 4H at approx. 90 mA. I would rate it at 45 mA, where inductance is 6.8H Peak output: 58v + 58v at 40 Hz. High frequency data (resistance for best available square wave at 5 kHz): push-pull: with a 7k source and 15k + 15k loads, it looks adequate, though there’s still 1.5 cycles of ringing around 60kHz - but the bass will be worthless, maybe -3 dB at 150 Hz (I didn’t even bother to measure it). With a 1700 ohm source, loads of 5k + 5k are needed to get a nice square wave. There’s only a tiny amount, about 1%, of high-Q ringing at around 250kHz. In this case, bass goes down to 70Hz at -1dB, 30Hz at -3dB. The highs extend to -1dB at 45 and 60kHz, -3dB at 75 and 87kHz. By far the best high end of the cheap units I’ve measured! single-ended: You can’t stop the ringing at all. The best compromise was with a source impedance of 700 and a load of 14k, but it still rings for 4 cycles at around 70kHz. Very similar results are obtained at 1700 ohms source and 20k load. The ringing is a little lower in level but lasts a bit longer if you reverse the primary leads and load the secondary with 5k (source 1700) but that’s a pretty heavy load for little benefit. Still, it does provide -1dB at 16kHz and -3dB at 40kHz. This is pretty good performance, if you can adequately drive it - say, with a type 45 or a 2A3 tube! More seriously, some of the television vertical output tubes like a 6EM7, 6DN7, or 6CK4 might work well here, or maybe a triode-wired EL84. In a single stage, possibly a 5842/417A or a 7788 (triode-connected) might work. It could, just barely, drive a pair of 2A3’s in push-pull to 40 Hz if the driver uses the full 45mADC capability. A 5842 at the “book” value of 150v and 26mA will run out of steam at 33 + 33 volts peak output at 40 Hz or 58 + 58 volts at 70 Hz due to the low primary inductance. Hurry! This offer must end December 31st, 1999! Hurry! This offer must end December 31st, 1999! Z-glow? ParaZen? A Doc B. Modded Zen 84B By Doc Bottlehead Intro by Brad Brooks Who else would you expect to take a perfectly great little SE pentode amplifier, and soup it up by parafeeding it? Don’t put anything past old Doc B. This will teach a guy about leaving anything on Doc’s workbench unattended! Why did he do it? Well, a number of readers asked him to—Doc aims to please. From deep within Doc’s newly remodeled dungeon, this editor obtained the following drawings and photos. What’s this all about anyway? Check out these mods: • C4S constant current source in the driver stage • Parallel-fed output stage • Reworked the ground buss to a single grounding point at the input jack • Power transformer was isolated from the chassis and the core was grounded at the input jack. • Tube rectifier out, ultrafast soft-start diode rectifiers in. • Diode reverse recovery spike filtering. • Schottky Diodes in heater supply! Doc uses the existing output tranny primaries as the parallel -feed plate choke. The secondary windings are connected as a sort of regenerative feedback loop. In addition, the driver tube plate is loaded up with a C4S constant current source. Not only a current source, this little board helps the 6N1P dual-triode driver operate at close to the theoretical operating points, as it sees effectively a These measurements were made after very high plate resistance. Another benemodifications were completed: fit of using these cool C4S boards is that they further isolate the driver from power • Power - 2.29 watts RMS ~ supply noise. 10%THD 1KHz 8 Ohm nonWith additional components added to the chassis, Doc helped the thermodynamic issues by creating a “heat drain” where the rectifier tube used to be. This, and spacing the base plate out with some hardware helps cool the innards. • inductive Hum & Noise < 20mV Tube operating points 6N1P 200V Plate 10mA -2V Grid Man, I can only imagine how much of Doc’s knuckle skin was left inside these little cuties... SV83 300V Plate 38mA -10.3 Grid How does it all sound? Try it and see! Be sure to send us the results of your hotrodded gear. son???? — no Is a low driver Zout only required for its ability to deliver drive current or are there other reasons? — As above, the frequency response is another consideration. What appear to be trivial basic questions soon seem to get pretty involved to me and I haven’t found the real answers easy to come by in any of the introductory texts I have looked it. A lot of this stuff seems to be skimmed over, an infinite grid impedance not requiring any current!! — yes. Sorry if this stuff is real basic but perhaps there are others like me who get OK results but don’t really deeply understand the issues and your responses may help them also. Cheers, Bart ( not too proud to ask :-)) TWELVE WAYS TO PARAFEED By Paul Joppa A recent thread on the Bottlehead forum asked about using parafeed with a cathode follower output tube (a 6V6. ed). The attempt to describe the circuit failed, partly because words are a poor substitute for a picture, but also because there’s lots of ways to connect a parafeed output. In fact, there’s six ways to do it for a regular anode load, and another six for cathode followers - a total of twelve ways! Figure 1 shows the twelve connections. How does one choose between them? Here are some considerations: 1. 2. 3. 4. 5. 6. DC voltage at the transformer primary. This is an important consideration when using transformers that are not rated for high voltages, such as line output transformers and multifilar wound interstage transformers. The primary may be grounded (safest), at cathode potential (reasonable if the cathode is close to ground, but DC coupled amps may have high cathode voltages), or at plate or supply voltage (needs a transformer rated for high voltage). DC voltage across the coupling capacitor. At audio frequencies, this is the capacitor voltage. At low frequencies however, some signal voltage may appear across the capacitor in addition to the DC voltage. The best way to estimate this is to simulate the circuit; however a reasonable estimate is that the signal voltage peak is no more than the B+ voltage. The cap should be rated for the sum of signal plus DC voltages. In some connections the signal loop is confined to the tube, cap, and transformer. Others may include the power supply or the cathode bypass caps, or both. Incidentally, if the loop does not include the cathode bypass cap, that cap can often be eliminated. Some configurations are said to just sound better, for reasons more subtle than the obvious circuit topology. This is a matter of experience, and our experience with parafeed is still limited, so listening to it yourself is still the most reliable approach. In the cathode-follower circuits (G) through (L), the bias resistor and bypass cap can be eliminated by choosing the choke DC resistance to be the right value to set the bias. In all cases, a fixedbias arrangement can be used, eliminating the cathode resistor and cap. Generally, the plate or cathode loading choke can be replaced with a current source provided it has enough voltage compliance. Figure 1. Twelve Ways to Parafeed. B+ B+ (A) B+ Circuit (B) B+ (G) B+ B+ (C) B+ (H) (D) B+ (I) A B C Primary DC voltage Ground Cathode B+ Capacitor DC voltage B+ B+, minus cathode Low D B+ B+ E B+ B+, minus cathode F B+ Low G H Ground Cathode Cathode Low I J K B+ Cathode Cathode B+, minus cathode Cathode Small L Cathode B+, minus cathode B+ B+ (E) B+ (J) (F) B+ (K) Signal loop includes: cathode bypass power supply and cathode bypass cathode bypass power supply and cathode bypass power supply power supply and cathode bypass power supply power supply and cathode bypass (L) Comment safest said to sound good said to sound good safest What I Wish I Had Known About Dual Volume Controls Before I Purchased... By Tom McDonald cussion of volume control ergonomics. It is a kind of discussion that many people might not have read before. I started ergonomic studies when I was a computer programmer who wanted to create programs that were simple to use. Ergonomics of Dual Volume Controls Over the last twenty years, every pre-amp or integrated amp that I had ever used had a single volume control and a separate balance control. I was familiar with this system and did not want to change. But some stereo equipment uses dual volume controls, one for each channel, and does not have a balance control. I finally purchased the Foreplay pre-amp kit with its dual volume controls. I thought I would hate this system, but I loved it, for the most basic of ergonomic reasons. So what are ergonomics? Ergonomics, as defined by the latest Webster Dictionary, is: “An applied science concerned with designing and arranging things so that people and things interact most efficiently and safely - called also human engineering.” The rest of this article hopes to communicate the point that the ergonomics of dual volume controls seems more normal, organic, natural, logical, and human. What follows is an industrial engineering type dis- The words "control" and "knob" designate the same control element, they are used interchangeably below. If we dissect the logic of the volume changing process, we find that with dual volume controls the volume is raised by turning clockwise with two hands, one hand on each control knob, or alternating between the knobs with a single hand. If the left ear hears too much loudness (compared to the right ear), the left arm and hand respond by turning back counterclockwise. Left side is always left side, right side is always right side, a clockwise turn always raises volume, a counterclockwise turn always lowers volume. The mind only has to think which side of the body to respond with. The arms and hands and ears function normally responding to their own side of the body. This is classic, simple ergonomics. Ergonomics of Stereo Volume Control and Balance Control But with a single stereo (dual channel) volume control and a separate balance control, the operator many times is trying to turn in opposite directions and thus can be confused. As the operator raises both channel's volume with a single volume control, by turning it clockwise, if the left ear hears too little volume (compared to the right ear) then he/she must turn the balance control counterclockwise toward the left channel to raise the left side volume. The normal clockwise rotational direction to raise the volume has been reversed to a counterclockwise direction by the balance control. The ergonomic problems here are that the arms/hands must respond in two different directions for the same function of raising volume. Clockwise for the volume control and counterclockwise for the balance control. Reversing the scenario, if the right ear hears too little volume (when the left ear hears correct volume level) then the balance control is turned clockwise which is the opposite of the left-ear-too-quiet scenario. So the balance control causes confusion by operating in different directions depending on which ear has the too-little-volume problem. In addition, as the balance control raises one side's volume, the volume of the other side is lowered even if the operator doesn't want to lower it. Usually this means that the operator responds by raising or lowering the overall volume higher and then adjusting the balance again to get the channels balanced at the new higher volume level. A complex adjustment cycling problem begins caused by the sometimesclockwise sometimes-counterclockwise operation of the balance control and the subsequent need to readjust the volume control. So dual volume controls are simpler to use mentally, although they sometimes require more physical effort, since you must always turn two controls to raise or lower the overall volume level. Once a balance control is set you may only have to use only one control, the volume knob, to change the overall volume level. Some sound systems need a different balance control setting for low, mid, and high volume levels due to speaker performance changes at different volume levels. In such cases the stereo volume control and separate balance control also require the adjustment of two knobs as does dual separate volume controls. So the work level in this case is similar. Probably the simplest mental/ physical process instructions for using the stereo volume control and balance control combination is as follows: 1) Turn up the volume knob while listening for the loudest channel. (I think that it is easier to detect which channel is loudest than which channel is quietest.) 2) Turn the balance knob to "send" the extra volume away from the loudest speaker. 3) Raise or lower volume and adjust the "send" until the overall volume level is reached and each ear hears the same volume level. "calculate" the true volume level by looking at two knobs is an irritation; it is also easy to forget to do. A Verses B Channel Comparisons I must admit the points made above are subtle, but subtleties are what high-end audio and ergonomics are all about. After adding up many fine points a general bias is produced of either overall simple or overall complex operation. Even though ergonomic considerations vary it can be generalized that thesimplest-is-the-best for most people. Obviously, ergonomic discussions can continue ad nauseam based on the needs, likes, and dislikes of the operator. Another advantage for dual volume controls is the ability to attach different speakers to each channel and then easily do a speaker A verses speaker B type sound comparison. Each speaker has its own identity in a separate volume knob. This system also helps compare component changes in one channel verses the other channel. This may not sound like much of a help but in truth it is much less work than with a volume control and balance control. With a stereo volume control and a separate balance control the operator must mentally calculate by first viewing the stereo volume knob's position then looking to the balance knob to see if the channel in question is raised or lowered by the balance knob position. When your mind is already busy checking speaker room position, looking for reflective surfaces that may be affecting the sound, and considering the circuit and/or part change that you made, the added need to But with dual volume knobs, that is a single knob for each channel, a single look is all that is needed to know a channel's true volume level Ergonomic Summary Overall I've found that dual volume controls are not much of a hindrance and are actually a significant convenience in many situations. Volume 1 - 1994 issues - $12 *** Introductory Special Until Jan. 5th - $10 *** a Williamson amp; Dyna Stereo 70 mod bake-off; converting the Stereo 70 to 6GH8's; a QUAD system; triode input Dyna MkIII; MkIII vertical tasting; smoothing impedance curves; Altec A7; Ampexes Nagras and ribbon mikes; Triophoni, a 6CK4 amp; audio at the 1939 World's Fair; books for collectors and builders; V. T. vs. R. M. A. cross reference; FM tuner tube substitutions; Big Mac attack – the MI200; 6L6 shootout; a vintage "audessey"; more FM tuner mods; vintage radio mods; Heathkit rectifiers; PAS heater mod. Volume 2 - 1995 issues - $15 *** Introductory Special Until Jan. 5th - $13 *** Rectifier shootout, tube vs. solid; FM 1000 recap and meters; single ended 10 amp; triode output W- 4; Optimus 990 - speaker for SE?; star grounds; tuner shootout; Living Stereo, vinyl or CD?; World Audio SE integrated; firin' up - smoke checking; Brook 12A schematic; 6C33 vs. 3C33; Heathkit power transformers; 6B4's + Magnequest = SEcstasy; W5 mods; triode operating points; Dyna restorations; Marantz 7, 8 and Scott LK150 impressions; hackable vintage gear; Quasimodo - PP 805 amp; restoring a Scott 340 in 75 minutes; a dream system for 78's; cartridges and styli for 78's; Restoring a Lowther, Part 1& 2; easy tube CD output hack; 6ER5 phono preamp; 304TL & 450TH SE operating points; hypothetical DC ESL amps. Volume 3 - 1996 issues - $15 *** Introductory Special Until Jan. 5th - $13 *** Single Watt, Single Tube, Single Ended, an amp for Lowthers; the Vintage Speaker Shootout of 1996, QUAD vs. Lowther, vs. A7; the Voigt Loudspeaker, the Single Ended eXperimenter's kit; cathode coupled SE 6AS7 amp; how to build the Superwhamodyne; refoaming AR woofers; mesh plate tubes; rebuilding QUADS; QUAD amp filter surgery; single gain stage amps; the Brooklet, and Brookson, choke loaded PP 6080 amps; transformer coupled PP 6DN7 amp; the Iron Maiden; Building the Lowther Club Medallion; the TQWT, a tapered pipe enclosure. Volume 4 - 1997 issues - $15 *** Introductory Special Until Jan. 5th - $13 *** the Whampipe/ Hyperwhamodyne; weird interconnects; winding your own SE output transformer; Tapered Quarter Wave Tubes; battery bias; onetuber 417A and 437A amps; DAC attack; 6BL7/ 211 SE amp; pro sound speakers at AES; 46 plate curves; what’s all this about parallel feed?; parafeed line stage; C. W. horn divided by two; Svetlana meets Brooklyn; parallel feed SE 811A amp; parafeed 2A3 amp; Lowther fixes; Altec vs. the competition; VSAC 97 program guide; VSAC 97 photos; Andy Bartha’s cool speaker cables; Paul Joppa’s 6DN7 driver stage; S. E. X. kit schematic revealed; an Edgarhorn builder’s story; direct coupled active loaded parafeed 45 amp; Brainiac’s S. E. X. changes; VSAC 97 seminar notes; tweaking the one tube 6DN7 amp, Lowther drivers, and the Wright preamp; 300B S. E. X. amp conversion; mini monitor for 300B amps. Volume 5 – 1998 issues - $15 *** Introductory Special Until Jan. 5th - $13 *** Blues Master part 1; Blues Master part 2; Strapping SE amps for More Power; Ron Welborne’s Parafeed 6EM7 Amp; Cool Technical Stuff from Brainiac; Brainiac on Load Impedance and Triode Operating Points; Blues Master Corrections; Meatloaf – an ineXpensive 94dB Speaker Recipe; Hotrodding the FM-3; A Visit with Brian Sowter; Load Impedance and Operating Points – Part 2; Soul Sister, a Parafeed Line Stage; Alan Douglas – When Tube Testers Disagree; Eric Barbour SV572-10 Line Stage; Load Impedance and Operating Points Part 3; A Turntable Odyssey, Part One; A Doc B Phono Pre(liminary), CD Treatments; Jim Dowdy 112A Parafeed Line Stage; VSAC 98 Photos! Available Soon Volume 6 – 1999 issues *** Introductory Special Until Jan. 5th! *** *** All Volumes 1994 through 1998 on One CD-ROM! Just $55 *** Prices do not include shipping and handling. Please allow 3-5 weeks for delivery. Bottlehead Reports This month we feature reports from the Valve group in Washington state, and the Tennessee Tube Enthusiasts. Rumor has it that there have been a couple of meets in Vancouver, British Columbia—perhaps we will be able to include a report from them in future columns. Also, check out the report from the Boston area group on the www.enjoythemusic.com web site. Sounds like a lot of cool fun...You got something going on? Send me your reports and photos—Brad. Valve Meeting, October 1999. Acoustical Magic -- Kirkland, Washington. Quest, our reporter in the field, reports: “Here's a brief report on Last Sunday's VALVE meeting @ Acoustical Magic (N. Kirkland) “Last Sunday the weather was cool but sunny. As usual I was wearing my smile on my face an joy in my heart to attend Doc's VALVE meeting at Acoustical Magic. “Being the first to arrive there (aside from A.M.'s Gil and Dorothy (Dorothy Harwood, owner) who were there to open up the shop at 11:00am) I swiftly introduced myself and took a short break in their largest showroom, listening to their demo gear with my own software. Shortly afterwards Doc showed up in his little pickup truck with a blue tarp over some "secret" stuff . Underneath was Doc's newly made Straight 8 with blackish "fakestone" speckled finishing on it. According to Doc he had these speakers finished last night and it hasn't been completely "run in" yet. He was confident that the sound will get better as the days went by...and I believed him. Along with his gizmos, tools, Foreplay and ParaGlows he also bought a pair of KR 2A3 along to play with. “John "Smoothplate" Tucker came along with his Sovtek 6B4G version of ParaGlow and his usual "bag of tricks": his own power supply, DAC, preamp, wiring, etc...” [Quest reports that typical Valve meeting activities went on: Coffee drinking, swapping around various combos of DIY gear and listening to your favorite tunes.] Quest continues…”Among us sat a sneaky little guy that didn't introduce himself until the midst of the listening session... Guess who? It's Vinylly! He silently brought over his Thailand-made all chromed 300B SET amp to audition: This baby consists of single 300B per channel, driven by 6SN7s and some small MT tubes (ECG6189W you say??). We played some Jazz vocals and it struck me with the sound that is typical with 300Bs: smooth, nonfatiguing soundstage with a strong authoritative sense in vocal presentation -- female vocals came out effortlessly with the finesse that is known mainly to DHT Single-Ended configuration. “Halfway into our fun-filling sessions came Hopper accompanied by Doc with 2 white boxes of unknown content, mumbled something like "...quick! stick'em in while they are still warm!!" " What was that?" I wondered. As soon as Hopper pulled out a tube for that box and proclaimed "...VV....2A3." Did I ever noticed that, and everybody was stunned just by the looks of it! Physically speaking those VV 2A3 looks more like a VV-52 to us. The glass envelope is twice the height of the typical ST tube and it's one and a half time bigger too. Of course the contents inside is proportionally bigger as well. Doc swiftly pulled out his KRs and put in those big Muthas. Wow! exclaimed Richard: "....these 2A3 sounded very good indeed!"… [I am excited myself to hear these 2A3s as well…there seems to be no lack of good new 2A3s out there for every budget…] “Thanks to Acoustical Magic for their place and various treats, Doc and Smoothplate's various gears, Vinylly for his super 300B SET (boy that baby sure is heavy!!). Best of all, Kudos to Hopper for his VV 2A3. Those tubes are a blast!! “We had so much fun that afternoon. I always leave Seattle with a smile of content in my face :^>” Tennessee Tube Enthusiasts, October 1999. Phil Sieg’s house. Knoxville, Tennessee. Phil’s got the scoop: “Well, it's really the Tennessee Tube Two right now. Brad Brooks drove over to knoxpatch this weekend with his stock Foreplay and ParaSEX. We listened to the T-1s for a while with the modified Atmas driving full range - the baseball playoffs are interfering with finishing the 45s - so Brad could get a feel for the "sound" of the system. Then we plugged in the Foreplay and ParaSEX monoblocks. Everything else stayed the same. First, 5 parafed Watts will drive the T-1s full range with relative ease. There was less extension and air on top, but the tonal quality of the midrange was right there. Lester's clarinet and Roy's trumpet (Laughin' to Keep from Cryin') had authority and body, and that "bright" Eldridge sound came across faithfully. Bass was not as deep as with the Atmas, but it was taut and well-controlled. Duke's piano (This One's for Blanton) didn't have quite the sonorous body as it did with the Atmas, but the attack and decay of the notes was all there. Same with Ray Brown's plucked bass. So what does $500 worth of electronics driving a pair of $13K speakers prove? First and foremost is that circuit topology is by far and away the most important factor in design of an amplification stage. Tube rollin' and boutique parts will only get you so far if the topo is screwed up. Second, there's a whole lot of pricey gear out there that would slink off, head hung in shame, when compared to this little combo. Did they best the Atmas? Well, no (and I think Brad agrees). But the Atmas are an exceptional pair of amps. However, my sonic memory tells me that the combo is every bit as good where it counts as my old ARC VT-150SEs (and I cringe inwardly as I think about the price tag on those). [Phil and his wife Tina took me out to a well known pub in Knoxville near the college. Never have I ever seen so many people wearing orange, the team colors of UT, and it wasn’t even game day! Man, this town sure loves it’s football…] Brad took some pictures, including one of my work-in-progress 45s, which will eventually show up in VALVE. And he shared his thoughts about what was next for his Foreplay/ParaSEX combo, but I'll let him talk about that. We talked about other designs (we have a shared interest in the KR PX-25 and talked about building ParaGlows that could accommodate a 2A3 and the PX-25). And we discussed how we can grow the Tennessee Tube Two. He going to try to set up something at Nicholson's Hi-Fi in Nashville soon. Then maybe something in East Tennessee again before Christmas. All-in-all, a very good day with good ideas for the future. Anyone in the area reading this who would like to participate, please e-mail.” [Sorry bottleheads, no pictures of the meet this time, but I promise to put them in the next issue.] Valve Meeting, November 1999. Rancho Tonalities -- Poulsbo Washington. Our tireless reporter Quest sends this report: “This time instead of driving to Rancho Tonalities alone by myself I dragged TonyD. along with me. We managed to hit the Edmonds ferry terminal for the 10:50am ferry and arrived around 11:45am, and before I reached into that evil Dungeon door I was so familiar with I heard some laughs and music pouring out from the basement....It wasn't until I walked down the stairs that I realized that there was a huge gathering this time. “Eager to introduce myself I waded through the crowd and talked to many other guys on the show: Paul Joppa, Cameron, Doc, Tim, "Willy the squid" Tony , Ed, John, Tony Glynn(Yes! Tony Glynn of Lowther America was here!!),Aaron and many others around. Looking straight down the end of the basement I saw the already broken-in straight-8. It sounded way smoother than our first encounterings in Acoustical Magic. Tony immediately pointed out that the sound is much more coherent than what he thought it would be, and the bass? plenty for all of us. We sat down while guys took turns sitting on the "golden" spot. From a distance I saw Doc's B-Glow playing with John's eXception and his own DAC + a Marantz CDP(?) playing music. This time we opt for mostly vocal stuff: Ella Fitzgerald, my little favourite Charlie Hayden, etc. The sound was nothing short of stunning as I would say…” [Quest describes the goings-on that are typical of a Valve meeting: Laughing, playing music, laughing, swapping out the latest DIY wonders, listening to music. And, as usual at a Valve meeting, a little surprise… ] “While 1/2 of the audionuts stucked to their chair on Doc's basement, others secretly "sneaked" upstairs to take a look at Doc's secret weapon: the Beveredge speaker system. This odd looking speaker comes as 2 planar structure and 2 "coffee-table" like subwoofer. According to Doc the array of ribbons on the planar structure plays down to 80Hz before the subwoofer takes over. With built-in amp (some sort of SEPP using 36KD6?) on each planar structure base all we could see is the RCA interconnect wirings and that's all. When Doc played some music through the system it sounded stunning! A full-range system that has the power to rock the house and and clarity is everything you'll always wanted, and more..... “We hanged around Doc's upper level as the rest of the people carefully sneaked into the basement: Lehman(?), a friend of Wendell in Japan showed up for a bit of fun, and so did Jay. They played Ry Cooder and V.M. Bhatt's "A Meeting by the River" with steel guitar and sitar and the sound was just marvelous: Ry's steel guitar has all the body and weight that is appropriate to the soundstage, without being overly "dry" nor "shrill" and definitely not edgy at all. With V.M.'s complement into the sonic picture everything was just perfect. (If it's because I have to drive home later that day I would have ask doc fo a glass of wine :^> “Queen Eileen was kind enough to prepare some "num-nums" for us (big applause for Eileen!!!) and brought home a big pot of Starbucks coffee. While the folks upstairs chomping down the dip and the spread we talked about many other things in the audio industry, people and dogs (Doc just brought home a big dog ...it is a blend between boarder-collie and ???) [Pony, Perhaps?] “Later with Tony Glynn and a few others in the kitchen area some of us went down to the basement afterwards and discovered that the crowd now played Charlie Hunter and Leon Parker's Duo, with Aaron sitting in the "golden chair" quietly listening to the tone and the color produced by the audio picture. Lehman (sorry bud for I might have spelled your name wrong) started talking about his recent problem with the hum from his SE-1. Eager to jump into the bunch I followed him and John Tucker to Lehman's bug (yes! a classical 1974 bug!) , picked up his amp and later John took off the bottom plate and took a quick look into it. He advised Lehman to have his amp reworked and instead of using 6SN7 try something else ..... “As dusk came little by little some of us left Rancho Tonalities and went home. Instead of intensive audio session this meeting was sort of casual gathering in nature: warm, friendly folks such as Ed. John Tucker, "Willy the Squid's warm smile, Richard and many others make us feel like one big family. (TonyD: are you coming next time :-) “Kudos to Doc and many other favourite guest like Tony Glynn, Paul Joppa and John Tucker, Cameron and Richard, Jay and TonyD., Tim and Ed, "Willy da Squid" and Lehman (I hope your hum problem will be over soon). “Also a big thanks to Queen Eileen's dip and other snacks! Take care!” Well, that’s all of the club reports and going’s on for this issue. I look forward to future reports, with photos of all of the fine projects and smiling faces enjoying everyone’s company and the cool music. Send them to me via my e-mail: [email protected] Until next issue... Entwined interconnect cable kits from Electronic Tonalities pre-cut twisted pair 20.5 guage High purity continuous cast long crystal solid copper conductors with a high temperature insulative coating, pre-cut polyethylene outer jacket and Vampire Wire RCA plugs $39 .5 per meter pair, $49 per 1 meter pair, $59 per 2 meter pair
