Published Quarterly , Price $9.00

Driver of Choice: The-ÓÈN7

Mid Priced

M r' Octal Licse -Sta e

A MA A-4 Kit Review

www.vacuumtube.com ISSUE 11 E D I T O R ' S P A G E A N D I N D U S T R Y N E W S

New tubes from Sovtek

VT V Issue # 11 New Sensor Corporation, New York, Table of Contents: New York has recently introduced a number of tubes for the guitar and hi-fi applications. Their new KT66 6SN7 Driver of Choice 3 and KT88 have the famous"coke bottle" shape reminiscent of the classic Tung-Sol Listening to 6SN7s 9 6550. According to New Sensor's press release, improve Octal Line Stage Project 10 ments have been made in grid and Richardson Electronics 11 plate materials used in their out- New 300B from Svetlana Mid-Priced Vintage Hi-Fi 14 put tubes. Svetlana Electron Devices, Huntsville, Computing with Tubes 20 The new Sovtek Alabama, has announced the availability 6550 comes in of their high-quality new SV300B power Tube Dumpster: 6688 21 two versions, the and its beautiful new packaging. 6550WD with a Russian engineers at Svetlana have worked ASUSA A-4 Kit Review 22 plastic base and hard to bring the quality construction, the 6550WE with materials, processing, aging and classic OTL Headphone Amp 24 the familiar metal sound to their 300B type. The plate is ring base. A new, carbonized, high-purity nickel and the fil- VTV Listens to 26 octal based, ament oxide coating duplicates the origi- directly heated tri- nal mixture. The gold-plated control grid Vintage Speakers in Japan 27 ode, the 6B4G is minimizes grid emission and improves also available from Sovtek. It is similar stability. It is available as a single tube or Test Bench: Power Supplies 28 in appearance to the Sovtek 300B, but as a Svetlana Tested and Matched Pair has a smaller bottle, octal base and a (pictured). For more information, con- FREDs and Schottkys 31 6.3V filament. We have also learned that tact: Svetlana Electron Devices, 8200 New Sensor will also be introducing a South Memorial Parkway, Huntsville, AL new 12AX7 type in late spring or early 35802 (256) 882-1344 2/27-28/99 Southern California summer 1999. Apparently, this is an Tube Enthusiast Weekend a Success improved version of earlier Sovtek Valley Launches New 12AX7 types. For more information, There was a good showing at the VTV Website contact: New Sensor Corporation, 20 Tube School with several industry profes- VTV recently uploaded its new website: Cooper Square, New York, NY 10003 sionals in attendance. The Hi-Fi Swap www.vacuumtube.com. Our site now 1-(800) 633-5477 on the following day was attended by gets over 7,000 visits daily! The site has about 1000 enthusiasts who found lots of many new features and products includ- tube gear, NOS tubes and parts. A great ing more information on and photos of time was had by all! VTV back issues, new tube links, buy-sell tube classifieds, etc. We have also expanded our Pro-Tube Shop catalog on- line with several new parts, accessories, tube amp kits and other goodies.

Cover illustration of 6SN7 structure by Kent Leech, a talented illustrator whose hobby is tube audio. lfy ou are interested in high quality technical illustrations, contact Kent at 925-253-9757 EDITORIAL STAFF Vacuum Tube Valley is published quarterly Copyright 1999 Vacuum Tube Valley"' for electronic enthusiasts interested in the and Big Tone' All rights reserved. colorful past, present and future of vacuum Charles Kittleson - Editor and Publisher No part of this publication may be reprinted tube electronics. John Atwood - Technical Editor or otherwise reproduced without written permission of the publisher. Subscription Rate: US$36/year (4 issues Eric Barbour - Senior Editor US$43/Canada & US$66/Asio, USS53 Europe Send circulation and editorial Terry Buddingh - Guitar Editor correspondence to: US Bank Check,Credit Cards or Cash Vacuum Tube Valley Steve Parr - Art Director are accepted for payment. P.O. Box 691, Julie P. Werner - Copy Editor Belmont, California 94002 USA Phone - (650) 631 - 6550 e-mail [email protected] FAX - (650) 654 - 2065 Website - www.vacuumtube.com ISSN # 1095-4805

V A C U U M T U B E V ALLEY IS S U E 11 6 SN 7: D RI V E R O F C H O I C E

connections on a top cap. Thus, it could be plugged directly into an older TRF 65N7: radio that used 201-As, while allowing K2 operation of the heaters from an external filament transformer, and eliminating the Driver of Choice K "A" . Marathon, Sovereign, By Eric Barbour Cardon/Sparton and Arcturus made simi- lar during the 1926-28 period.

©1999 All Rights Reserved The Brits were a bit late here. Prominent engineer H. J. Round devel- oped a similar cathode around 1922. with mini- Why are we doing an article about this Round's AC triode had space as the insu- dual triode? It's not used in modern guitar mum hum lator between the bright emitter tungsten amps, and it's not common in high-end induction heater and the the cathode. This slow- into the equipment. This lack of use is not ger- warmup version was first developed into a audio or mane to its worth! The 6SN7 was a semi- product by MOV engineer C. W. nal audio type. First, it was the driver radio circuit Stropford and used in their KL1 triode tube in the first American version of the (especially (1927). However, the Stropford cathode's n the criti- Williamson amplifier. This was the first heater was wrapped around a silica rod widely-used "hi-fi" amplifier design of the cal detector and was not in direct contact with the stage of a postwar era. Second, a good 6SN7GTB nickel tube. Met-Vick engineer E. Yeoman TRF or will give almost any other medium-mu Robinson produced a slip coated heater triode a run for its money, in terms of lin- superhet and nickel tube assembly which was a earity. receiver). A quick warm-up type. It was first used in side benefit Met-Vick's AC/R and AC/G tri- 1. History was that odes(1927). MOV later bought in this plenty of The first primitive directly-heated tri- design and re-numbered it KH1, aban- electrons odes were usually low-mu or medium-mu. doning the KL1 and Round's design. Many kinds of cathodes were under devel- were emit- 6N7G opment at the time, but their invention ted by the Standardization arrived with RCA's UY- became dominant. It was a high-purity oxide mix- 227 (1927). Its design, and its five-pin nickel tube coated with a mixture of bari- ture, as much as an oxide-coated filament. base, became industry norms. The 227 um and strontium oxides, binders and Result: good efficiency and low hum, plus was the father of all subsequent medium- other agents. By inserting a wire heater a cathode that could be connected to its gain triodes. Although used only as detec- into a ceramic tube (or, later and most own bias resistor, allowing the tube to tor/audio preamp stages at first, it became commonly, coating it with aluminum self-bias and eliminating the "C" bias sup- critical to the development of television, oxide), and then slipping the heater into ply. radar, computers and a wide range of the nickel sleeve, the cathode could be other electronic applications. A problem The Uni-potential indirectly heated heated to a suitable temperature to make with RCA's ceramic cathode was an elec- cathode is credited to A.M. Nicolson of the barium-strontium mixture emit elec- trochemical reaction with the tungsten Western Electric and was first made in trons into the vacuum. The optimum sur- heater. The 2.5V early heater standard 1914. Its patent was applied for in 1915 face temperature was found to be about was a fix, but heavy heater current was a and was issued in 1923. Its successor was 900-1100 degrees Celsius. disadvantage. Of all the 27s around in the McCulloch/Kellogg 401 (1925). It the late 1920s, the Arcturus was thought A major advantage of this scheme: the was a plug-in replacement for the com- heater could be run from low-voltage AC, mon 201-A triode, except with AC heater

Types: 227, 56, 76 and 6J5G Types: 6C8G and 6F8G

V AC U U M T UBE V ALLE Y ISSUE 11

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to be the best for RCA's 6J5 (1937) enjoyed much more quick heating and low popularity, pushing aside the 6C5 in con- hum. sumer equipment. It was also used in mil- itary equipment from World War II until The UY-227 led to the 1980s. the 27 and 37 (1932), which led to the 56 Shortly thereafter came the first medi- and the 76 (both um-mu DUAL triode for small-signal use: 1932). The first such RCA's 6F8G (late 1937). It had the grid tube to use a 6.3V of one triode connected to a top cap, heater, the National apparently because radio engineers wanted Union NY67 (1931), to keep the detector stage's grid as far did not enjoy as much away from the AC heater power as possi- success as the later ble. A similar type, with higher mu, was type 76 did. The 6.3V the RCA 6C8G (1937). Although the RCA 6SN7GT/V7:231 (1940s), 6SN7GT (1940), 6SN7GTB (1960s) figure was chosen to 6C8G was used in the first electronic work off the extant computer, ABC, (see VTV #7 pp 28-30) automotive batteries (a these first octal duals were not big suc- typical lead-acid cell cesses in other areas. produces 2.1 volts when fully charged, A peculiar development of 1938 was and car batteries of the the National Union 6AE6. It contained day had three cells). It two very different triodes, one having a became the most pop- variable-mu grid. It was designed to drive ular standard for paral- the 6AD6 eye tube directly in a radio cir- lel heater connections, cuit. Variable-mu tubes are unsuitable for even in radios not used high-fidelity use because of their high dis- in a car. To this day, tortion. "filament" transform- There were dual triodes long before the ers are made with sec- 6F8G. These were usually special power ondaries in multiples triodes of one type or another. One major of the same 6.3v fig- line, which died out after WWII, was the RCA 6SN7GTA(1960), GE 6SN7GTB (1960s), RCA 6SN7GTB (1975) ure--even though they Class-B push-pull dual triode family. It usually run solid-state started with the 19 (1933) and went electronics nowadays, through many variations to the 6N7 and not tube heaters. (1936). Also predating the 6F8G were the The 56 and 76 were many duals which had a driver triode and slowly pushed aside by an output triode in the same envelope. the new-fangled octal Usually they were intended for direct cou- base. It allowed many pling, with the power triode being more connections to designed for zero-bias operation. This more complex tubes, included the Speed Triple-Twin and the setting the stage for 6AC6. We will go into high-mu triodes multiple triodes and such as the 6SL7 in a future article; they the like. RCA's 6C5 came later than medium-mu types. (1935) was the first The 6F8G's child enjoys massive suc- octal triode. Early cess, and is still being manufactured and metal 6C5s were KenRad 6SN7GT (1940s), Tung-Sol 6SN7GT (1950s), used in new designs at the end of the mil- apparently just triode- CBS 6SN7GTB (1950s) lennium. RCA's 6SN7GT (introduced connected 6J7 pen- late 1939, officially registered with RMA todes. Tung-Sol intro- 1941) was the right package at the right duced the similar time. The grid cap was eliminated, as 6P5G (1936) as a radio engineers realized that it was not competitor. Tungsram really needed. It and the cognate in Europe made a 12SN7GT saw wide use in military 6C5G with a true tri- equipment during the war. ode assembly a little later. Neither one was 6SN7GT Ratings Escalation especially popular, since high-gain Type Vpmax Diss (per triode) tetrodes and GT (1939) 250v 2.5w were much more use- GTA (1948) 450v 5.0w ful in stages of a receiver other than the *GTB (1952) 450v 5.0w audio detector. *(controlled warmup version) Tung-Sol V7:231 (1945s), 6SN7GTB (1950s), 6SN7WGTB (19609

V AC U U M T UBE V ALLE Y ISSU E I 1

4 6 S N 7 D RI V E R O F C H O I C E

Special versions of 35, not 20 like the 6SN7, however). The the 12SN7GT were ECC32 (made by Mullard with the ST- made for low-plate- shape) was used in early Lowther ampli- voltage operation in fiers, but otherwise, was an industrial tri- battery and aircraft ode, like the ECC31. The ECC32 and radios. These were ECC35 were used by Pye and Leak, but often run from 26 no audio use of the ECC34 was known. volts, which was avail- able from aircraft 6SN7 variants included the British mili- magnetos. To save the tary CV181 and CV1988, plus the long- bother and mainte- defunct MOV B65. There are a number nance headaches of of B65s branded by Osram or GEC, but using a dynamotor or they were all made by MOV if British. vibrator to boost the Note that the B65 has a unique structure voltage, many low- and is not exactly a 6SN7. The CV181 Sylvania 7N7 (1940s), 6SN7GT (1940s), 6SN7GT (1940s) voltage tubes appears to be the only member of the appeared. Aside from 6SN7 family to appear in an ST-shape RF pentodes and envelope with a shoulder. 6SN7s were beam-power types, manufactured in Russia and China under this series included the Russian designator 6N8S (looks like the Tung-Sol 6H8C, because it is in Cyrillic lettering). 6AH7GT and Manufacture of 6SN7s has been con- 12AH7GT (1941) firmed in Italy, France, Holland (by and, after the war, Philips), Australia, Germany, Japan, India, RCA's 12SX7GT various countries in Eastern Europe, and (1946). even in South America. The original late 1940s British Williamson used Sylvania was a either an MOV L63 (6J5G) or the B65 determined competi- as driver tubes. tor to RCA, and pushed their Loktal After wwii, television and high fidelity types hard. Even so, came into the fore. Since low distortion was needed for both hi-fi and for the ver- Sylvania 6SN7W (1942), 6SN7WGT (1950s), 6SN7GTB (1950s) Loktals did not become standards to tical oscillator circuits in TV sets, the the same extent as the 6SN7 saw some duty in both worlds. In octal tubes. One of fact, a 1958 article (see ref. 5 below) the first Loktals was demonstrated that the 6SN7GTB was the 7A4 (1939). Like superior to the 12AU7 as a power tube many other Loktals, it driver in hi-fi amps. The 6CG7 (RCA was a blatant copy of 1954) was touted as a 9-pin equivalent of a pre-existing octal the 6SN7. It is notable in having an elec- tube (6J5). The 6SN7 trostatic shield separating the two sec- copy was the 7N7 tions. The later and more common 6FQ7 (1940). Both appeared eliminated the shield, probably to cut in 12-volt heater ver- costs. CBS-Hytron came out with the sions, as 14A4 and 12BH7 in 1950 as a higher transconduc- 14N7. The 7A4 and tance 9-pin version of the 6SN7. 14N7 were also avail- Although eclipsed by the 6FQ7 later, this able in special low- higher perveance version re-surfaced in the 1960s as a 6-volt version: the 6GU7., Mullard CV-181, Telefunhen 6SN7GI; Raytheon 6SN7WGT(1950s) capacitance versions, XXL and XXD. intended for color TV sets.

Mullard introduced The only premium version of the 6SN7 the ECC30 series dur- to be made for critical applications in the ing WW2. The USA is believed to be RCA's 5692 (1948), ECC31 came first, a member of the "Special Red" line. then the ECC32. Intended for avionics and military appli- The ECC31 is electri- cations, the 5692 was deliberately under- cally the same as the rated to maximize its lifetime (provided ECC32, but has a the engineer stuck to the ratings). RCA common cathode. No may have developed this tube, yet it seems ECC30 series are that GE actually manufactured it for them exactly equivalent to under contract. The distinctive red base is American 6SN7s, but apparently unique to GE production. there are some simi- Many other firms (including Raytheon, larities. This includes CBS/Hytron, and Rogers in Canada) the ECC33 (the µ is made their own 5692s, but always with Mullard ECC33 (1940s), ECC33 (1950s), 6SN7GT (1960s)

V AC U U M T UBE V ALLE Y ISSU E 11

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brown Micanol how much this "super tube" looks like a bases. The 5692 was period Sylvania 6SN7. And unfortunately, made in Sweden by the major manufacturers introduced the Standard Electric as 6BL7, 6BX7, 6DN7 and many other vari- the 33S30. This tube ants for vertical oscillator use, causing the was not widely used 6S78's market to wither. (and NEVER in audio, until the Some classic hi-fi amplifiers used the 1980s), except in 6SN7, though it had nearly disappeared one major applica- in new designs by 1960. Examples would tion. Read THE include: Bell 2145 and 2200, Bogen SAVAGE ART article D010 and H010, Brook 10C and 12A, in the next issue of Craftsmen C-2, 400, 450, C500, C500A, VTV for more on C550, Eico HF-22, HF-35, HF-50, HF- Brimer CV-1988 (1950s clear), Brimar CV-1988 (1972 tall), this. 60, HF-87, HF-89, ST-70, Grommes M OV B65 (1950s) 215BA, Goodell ATB-3 and NSA-20, Ironic--the current Harvey Radio HR-15 Williamson Amp, worship accorded to Heathkit W-1, W-2M, W-3M, W-4AM, this tube by audio- A-7, A-8A, Interelectronics Coronation philes is mainly due 100, Leak TL-12, McGowan WA325, to the use of its high- McIntosh 20W-2, Pilot AA-901 and AA- mu brother 5691 in 904, Sargeant Rayment SR-570, Scott the MFA 210A, 210B, 220A, Stancor Williamson Luminescence pre- kit, Tech Master TM15A Williamson kit, amp in the 1980s, UTC W-10 and W-20 Williamson kits. followed by a 1992 article about it in Not to mention a few early FM tuners Sound Practices by Sargent-Rayment and Browning. magazine. There was Please note that most of the above models a small following for were top-of-the-line for those companies "Special Reds" in in the 1946-1956 period. It should be Japan before this, but obvious that there was a strong reason to RCA JAN 5692 (1950s), RCA 5692 (1950s), CBS 5692 (1950s) no known Japanese use the 6SN7...possibly that it was the equipment specified best tube for the best amplifiers. Perhaps it. the miniature tubes took over for eco- nomic reasons, not for reasons of superior 6SN7-GTB 6SN7-GTA A highly obscure quality. And quite often, the manufactur- GE 6SN7 GTA/GTB Data Sheet (1954) 12SN7-GTA ET4899 company, Sheldon ers went over to the 6SN7's miniature Page 3 Electric Co. of cousins, the very similar 6CG7 (RCA,

CHARACTERISTICS AND TYPICAL OPERATION Irvington NJ, intro- 1949) or the somewhat different 12BH7 CLASS At A MPLIFIER, EACH SECTION duced a premium (GE, 1950). Plate Voltage 90 250 250 Volts Grid Voltage o —12.5 —8 Volts 6SN7 for use in TV Amplification Factor 20 20 sets in the mid- Few guitar amps and music devices Plate Resistance, app roximate 6700 7700 Ohms used 6SN7s. Gibson was fond of using Tronsconductance 3000 2600 Micrenhos 1950s. Most TVs Plate Current 10 1.9 9.0 Milliamperes "unusual" types. The Gibson BR-6, BR- Grid Voltage, approximate before 1955 used a 16=10 Microamperes —.7 —18 Volts 6SN7 as the vertical 6F, BR-9, early GA-40, GA-50T and the oscillator. So, Clavioline and GA-46 accordion amp had Heater warm-up time is defined as the time required in 6SN7s. So did some Hammond organs the circuit shown at the right for the voltage across the heater Heater Sheldon introduced terminals to increase from zero to the heater test voltage of Tube and Leslie speakers. (Vu). For this type, E=25 volts (RMS or DC), V,=5.0 volts under the "Hi-Po 6S78" for (RMS or DC), and R=31.5 ohms. E Test t Without external shield. such use, claiming all The big exception here is the pre-1956 kinds of supernatural PA amplifier. Literally scores of models 2 For operation in a 525-line, 30-frame television system as described in "Standards of Good Engineering Practice Con- performance advan- cerning Television Broadcast Stations," Federal Communications Commission. The duty cycle of the voltage pulse must not had 6SN7 drivers for the power tubes. exceed 15 percent of one scanning cycle. tages for this tube § Value given is to be considered as on Absolute Maximum Rating. In this rose, the combined effect of supply voltage Included are models by Altec (1570 fami- variation, manufacturing variation !eluding components in the equipment, and adjustment of equipment controls should not (along with a few cause the rated rolue to be exceeded. ly, 1520A, 1530A, and A256), Bell, tr In stogro operoting with grid-leak bias, an adequate cathode-bies resistor or other suitable means is required to pro- other versions of Bogen, International Projector tect the tube in the absence of excitation. common TV tubes Corporation, Masco (frequent use of which they tried to CLASS A RESISTANCE COUPLED AMPLIFIER either 6SN7s or 7N7s), Operadio, market at the same Op i; Re Ebb = 90 V.I ts Ebb = 190 Vol ts Ebb 0 300 V Its Newcomb, Rauland, RCA, Stromberg- Meg. ling• irs9. k gain En Rk gain Eo Fik Gain Eci 0 C C time). Sheldon 0.10 0.10 0.10 5300 10 10 5600 11 20 3030 /1 30 Carlson, and Thordarson. It is shocking 0.10 0.24 0.10 0403 11 14 4700 12 27 4400 12 41 Esig goi RP Rs . claimed in the 0.24 0.24 0.10 9400 11 13 8700 11 25 8700 12 58 to see how often the 6SN7 or the high- 0.24 0.51 0.10 11000 11 17 11000 12 32 11000 12 48 I Rk 6S78's box insert 0.51 0.51 0.10 19000 11 15 18000 12 29 18000 12 43 e , , mu 6SL7 was seen in these "low-quality" L. •-• - = 0.51 1.0 0.10 24010 11 19 25000 12 57 25003 12 54 ' , Ebb that it would "Make 0.24 0.24 10 0 14 12 0 16 20 0 17 28 Notes gotmlI ts expeattere It) shfeld be equipments. 0.24 0.51 10 0 14 16 0 16 271 0 17 40 selected to glee deslr 4 frequency Pictures Bigger, More 0.51 0.51 10 0 14 15 0 15 26 0 16 58 response. Ph should be adequately 0.51 1.0 10 0 14 19 0 16 35 5 16 52 br-prssedi Stable!" than a stan- 2. Tests note i 1. . is mangsuin R..is u Itage outp t fo five parr nt .5t, tot., harmonic distortion. 2. 6eln measured dard 6SN7 without at 2.0 volts mus output. 3. For z ro-bise data, pant rat r impedance in neg I igible. Table 1: distortion of medium-mu single offering a shred of and dual triodes. proof. It is amazing

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*-good used tube. B+ was 250v regulated, frequency 1000 Hz. "Syl tri"=Sylvania tri- angle plate construction, "triode"-tested the triode in a triode-. If the 3rd harmonic was less than 0.015%, it has been left blank.

Arranged in order of increasing second harmonic distortion. Tubes with the same distortion reading are not arranged in any particular order.

Type Rp used 2nd 3rd +76 Syl 40s* 37k .002

+5687 RCA sos. 48k .005 6CG7 Syl 60s* 25k .005 +9002 KenRad 40s 48k .005 +76 RCA 40s 37k .005 12SX7 RCA 1955 37k .005 12SX7 RCA 1955 37k .005 +5687WB Syl 1983* 48k .010 +396A WE 60s 25k .010 6C5G TungSol 30s* 37k .010 76 Arcturus 40s 37k .010 .017 OUNTAINHEAD OF M ODERN TUBE DEVELOPMENT IS RCA +6GH8A tri Syl 80s 12k .012 5814A Syl 70s* 37k .012 .015 RCA SPECIAL RED TUBES 6SN7WGTA Syl 82* 48k .015 6SN7WGTA Syl 78* 48k .015 Minimum life -10,000 hours! +396A WE 60s 25k .015

+C-327 Cunn 20s 37k .015 .017 • Another RCA First . . . these new tubes with a minimum life of 10,000 TABLE OF RECEIVING-TYPE COUNTERPARTS Special Red Tubes are specifically hours when they are operated within +56 RCA 30s 37k .015 5691 651.707 designed for those industrial and their specified ratings. Extreme care (0.6 A. hewer)tu3 A.A.'s«) 6CG7 JAN Syl 69* 25k .015 commercial applications using small- in manufacturing combined with 5692 65N7G7 type tubes but having rigid require- precision designs account for their 5693 6557 RCA Specie: r*s1 Tubes son be used es replace- 6SN7WGTA Syl 86* 48k .020 ments for reliability and long tube life. unusually close electrical tolerances. ren;111º7 Z ertre rn, t ee r z e w, 6SN7WGTA Syl 83* 48k .020 As contrasted with their receiving. RCA Application Engineers will be and excepHonel stability epe needecL 6SN7WGTA Syl 86* 48k .020 tube counterparts, RCA Special Red pleased to co-operate with you in Tubes feature vastly improved life, adapting RCA Special Red Tubes to END FOR FREE 6SN7WGTA Syl 83* 48k .020 stability, uniformity, and resistance your equipment. Write RCA Corn. AULLETIN-Bookles to vibration and impact. Their unique merdai Engineering, Section 57FR, SRB-1002 provides complete dace on 6SN7GTB Fuji 60s* 48k .020 structural design makes them capable Harrison, N.J. For RCA Special Red RCA Special Red Tubes. For your 6SN7GT CBS 54 clr* 48k .020 of withstanding shocks of 100 g for Tubes to be used as replacements in copy write to RCA, extended periods. Rigid processing equipment now in use, see your local Commercial Engineering, Section 6SN7GTB GE 70s* 48k .020 and inspection controls provide these RCA TUBE DISTRIBUTOR. 57F14. Harrison.N.J. B65 Genalex 1950s* 48k .020 T U B E DEPA RT ME NT 6SN7W Syl 1940s* 48k .020 5692 RCA red* 48k .020 RA DIO CORPORATIO N of AMERICA N A R RIS O N, N. J.

AVERAGE PLATE CHARACTERISTICS AVERAGE PLATE CHARACTERISTICS 6SN7GTA 6SN7GTA EACH SECTION EACH SECTION 28 350

E, - RATED VALUE E A RATED VALUE 24 300

20 250

16 200 el

12 150 111111•••••••••• ......

100

AlSe •111 1 ...... 50 .. ..gnegefausi, 11 1...... 100 200 300 400 500 200 300 400 500

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7 6 S N 7 D R I V E R O F C H O I C E

5692 CBS brwn 60s* 48k .020 so that this test was not especially helpful 5692 CBS brown 60s* 48k .020 in discerning different 6SN7s from each w ww2.netcom.comi-handmade/ 6SN7GT GE 1945 48k .020 other. first. html Check it out for new stock, sales, small 6SN7GT Syl 50s top* 48k .020 2) Similar miniature dual triodes were quantity items/closeouts, specials, 6SN7GT RCA 40s sd 48k .020 usually less consistent and often had high- technical help and a magazine index for 6SN7GTB West 1962 48k .020 er distortion than 6SN7s. projects. +6J6 RCA 50s* 25k .020 3) The forgotten 12SX7GT is VERY Cera fine 2x47uF/500vdc- $16.50 6CG7 RCA 1959* 25k .020 interesting. Hammond NEW: 300BX power- +UY227 RCA 20s 37k .020 .015 ( for 300B ) w/ universal primary- $136.36 ea. 6SN7GTB Rayth 60s* 48k .022 4) So are the old radio types 27, 56 and 2 e115.38 ea. Hammond's Improved SE outputs-1627/28/29SE- $105.45 ea., 2/$91.68 ea. 6SN7GTA Tele 50s 48k .022 76, as some DIYers have already discov- MaeneQuest B7 parallel feed pre-amp ered. 6S78 Sheldon 54? 48k .022 output transformers S65.00-$99.00 ea. CV1988 Brimar 50s* 48k .022 We also stock MagneQuest's matching chokes. 5) As might be expected, the Russian MagneQuest parafeed power outputs available. CV1988 Brimar 50s 48k .022 Kaluga 6SN7 is inferior to old-stock limber 4TC $5.28/ft, 10tH- 55.05/ft CV1988 Brimar 50s 48k .022 units. Cardas, Hovland, NOS tubes, Tube Sockets & 5692 CBS brown 60s* 48k .022 much more! Discounts for smaller users. One other item: the British versions Good buys abound in our free +ECC33 Mul 60s blk base 48k .022 tended to have a little more voltage gain ce'Product Flier No.1 9e 6SN7WGTA Syl tr 1986* 48k .025 than the American tubes. Otherwise, their •HANDMADE ELECTRONICS• 6SN7GTA Tele 50s 48k .025 measurements were not especially differ- P.O. BOX 9 1 14 ent. This may account for the "vast" 6SN7GTA Raytheon 50s* 48k .025 ALLENTOWN, PA 1 81 05-9 1 14 improvement in sound quality claimed for 6SN7GT KenRad 40s 48k .025 (Birthplace of the transistor) these tubes. Whether they are worth the 5963 RCA 50s 25k .025 .035 Voice: 610-432-5732 extra money is up to the consumer. 5814A JAN Syl 70s* 37k .025 .025 Since 1992 Vha/MasterCard/Discoyer +27 Philco/Syl 20s 37k .025 3. Outro -Export friendly - Friendly )service- 6J5GT TungSol 40s 48k .025 The 6SN7 has enjoyed almost 60 years +ECC33 Mull 50s brn 48k .025 of manufacture. Even so, it is used only in +ECC33 Mull 50s brn 48k .025 a few high-end preamps and power amps 4 • 6SN7GTB GE 70s* 48k .027 today. The world consumption is less than 6SN7GTB GE 66* 48k .027 10,000 pieces per year--not enough to jus- tify low-cost mass production. The only 6SN7GTB GE 58* 48k .027 remaining source, Voskhod Kaluga in +6BQ7A GE 70s 25k .027 Russia, recently closed its doors due to the 6CG7 RCA 60s* 25k .030 poor economic situation there and the 6SN7GT Tung 50s 48k .030 low demand for the tube elsewhere. If 6SN7GTB RCA 60s 48k .030 audiophiles want to save this classic high- 6J5G GE 3os. 48k .032 linearity tube for the future, they should get busy and start creating a viable 6SN7/6N8S Russ 90s 48k .032 demand for it. 6SN7WGTA Syl 80* 48k .035 +5687 RCA 50s* 48k .035 References CV181 Mollard 52 ST 48k .035 1. 70 Years of Radio Tubes and Valves, CV181 Mollard 52 ST 48k .035 John Stokes (Vestal Press, Vestal, NY, +6BQ7A Syl 60s 25k .035 .015 third edition, 1992), pp. 55-63. 5814A GE 5-Star 68 37k .035 .035 2, Tube Lore, Ludwell Sibley, 48k .037 Call or Fax Don Singerhouse 5687WB GE 1965* Flemington NJ, 1997. +417A WE 60s 12k .037 6CG7 RCA clear 60s 25k .037 3. Tube Data Manual, Sylvania Electrical Products Co, 1941. +5687 RCA 50s* 48k .040 (715) 246-3899 +6BF7W Jan Syl 1964 37k .042 .015 4. History of the British Radio Valve to 6SN7/6N8S Russ 90s 48k .042 1940, Keith R. Thrower (MMA +7199 triode GE 70s 37k .045 .030 International, Ropley, Hants. UK, 1994). +5687WB JAN Syl 85* 48k .055 5. "Distortion In Audio Phase Inverter 48k 12BH7 Syl 60s* .055 And Driver Systems," W. B. Bernard, l'.11\IGERHOUSE += Tubes not related in characteristics IRE National Convention Record, 1958, to the 6SN7. 4 Part 7, E 87. / OUND The results speak for themselves, but to Many thanks to Phil Taylor in England, I BOX 321 summarize: Charlie, John Atwood and John Eckland for New Richmond, WI 54017 1) Old-stock 6SN7s were remarkably con- fact-checking and other information. sistent from sample to sample--so much

V AC U U M T UB E V ALL E Y ISSU E 11

8 L I S T E N I N G T O 6 S N 7 s

Raytheon 6SN7WGT (brown base 1950s). A very musical tube with excel- Listening to 6SN7s lent detail, huge bass, mids were very By Charles Kittleson and Eric Barbour revealing. This bottle was well-balanced and very fast. Consider this one a top © 1999 All Rights Reserved performer. Rating 96 Sovtek 6SN7GT (1990s Russian). A There are literally hundreds of 6SN7 thinner mids. However, the highs were bland and primitive sounding tube. Not types, both domestic and foreign. For not quite right and seemed somewhat very musically involving and nothing spe- this listening test we auditioned several congested. Rating 84 cial. Used by tube amp OEMs due to its common US types and a few British types cheap price and ready availability. Rating that were made available to us for this test GE 6SN7GTB wafer base (1970s labeled 70 by tube dealer Kevin Deal of Upscale RCA). The worst sounding 6SN7 we lis- Audio. tened to in this test. Noisy as hell, sibi- Sylvania 6SN7W (metal base ring, top lant and distorted with harsh highs. To getter early 1940s). An early type with a Our listening panel consisted of: Eric add insult to injury, it was very micro- very smooth, well balanced sound. Barbour, Steve Parr, Dave Wolze and phonic. Rating 60. Presentation was clean, but there was less myself. It was conducted in the VTV lis- gain than others. Fantastic detail, very tening studio with the following equip- MOV B65 (aluminum base 1950s). A tight/clean bass with superb accuracy. ment: VTV Octal Line Stage, Pilot tube with excellent mids and great detail. Rating 97 SA232 basic EL84 stereo amp (rebuilt), Very clean sounding with above-average Sylvania VT-231 (bottom getter WWII B&W DM110 speakers, Sony CD player bass and highs. Rating 90 and Monster Cable speaker wire. era 6SN7). A well-balanced sound with Mullard CV181 (ST shaped 1952). This good imaging and forward mids. As with the previous issue of VTV is a very well-balanced tube. Great detail Presentation was very smooth and musi- (#10), we are using a number to rate the and very romantic with zero harshness. It cal, but bass was a little weak. Rating 95 tubes in this evaluation. Tubes rated in also had very deep bass. An exceptional the 90s are musical and sound excellent, tube. Rating 97 Sylvania 6SN7GT (top getter, black base tubes in the 80s are very good, but have early tri-plate 1950s). A musical and Mullard ECC33 (1955 thin brown base minor deficiencies, tubes in the 70s are easy-to-listen to tube with sweet detailed with very small plates). Slightly more highs. Bass was very good and imaging only acceptable and anything below that gain than other Mullard types. This one is poor. Note that tubes from different was excellent. Rating 95 is very detailed and fast with smooth batches and different years of manufacture response. Bass is flat and weak, which Sylvania 6SN7WGT (brown base with can sound different even though they may appeal to some audiophiles. green lettering, top getter early 1950s.) come from the same manufacturer and Rating 86 Very clean, dry and "military" sound. have the same structural design. This is Sibilant highs with humped bass. due to material and quality issues. We Mullard ECC33 ( brown base 1957). However, it was extremely detailed and have found that tubes made in the 1980s Very prominent, but distorted bass, slight- fast. Rating 89 and 1990s are more primitive sounding ly bright with thin highs. Rating 84 than those made in the 1940s through Tung-Sol VT-231 (very early, round black 1960s. Mullard ECC33 (smoked glass 1960s). A plates, smoked bottle 1945). This tube tube with somewhat less gain. Highs are had lower gain, was sibilant, but was very Listening Results a bit blunted, but midrange was warm. detailed and had excellent highs. Rating 84 Brimar CV1988 (brown base 1950s). Rating 92 Similar to the B65, but brighter and more RCA 5692 (red base 1950s). This tube Tung-Sol 6SN7GT (round mica side detailed sounding. Rating 93 had low gain and somewhat weak mids. spacers 1940s). A tube with nice detail Detail was very good, bass was fat but Brimar CV1988 (brown base 1972). An and musical mids. Bass and imaging were indistinct. Transients were excellent. excellent sound stage with a very satisfy- well above average. Rating 90 Rating 92 ing and musical presentation. Bass was Conclusion not as tight as others, but still a top-rated RCA 6SN7GTB (staggered black plates tube. Rating 92 1950s). A very romantic sounding bottle Without a doubt, the best sounding, with somewhat distorted and fat mids. most musical tubes in this test were the CBS 5692 (brown base 1959). This one Highs were weak and recessed. This one Sylvania 6SN7W (metal base 1940s) and had about average detail, but better bass might be a choice for listeners with sensi- the Brimar CV181 (ST shape 1950s). than the RCA 5692s. Gain was a little tive horn speakers. Rating 85 These tubes were exceptional performers low, but it was fast sounding with very in our listening setup. Unfortunately, sweet mids. Rating 92 Philips 6SN7WGTB (tri-plate 1986). they are very rare and can be expensive. A This tube sounded slightly bright with more readily available alternative would be GE 6SN7GTA (1953). A tube with nice good, but not 3D mids. Detail was good imaging and a romantic, satisfying sound. either the GE 6SN7GTA (1950s) or the and bass response was tight. Last of the early Sylvania 6SN7GT (1950s). Later In addition, it had powerful bass and US made 6SN7s from the old Sylvania Sylvania 6SN7WGTs were not as "magi- detailed, accurate mids. Rating 94 plant in Emporium, Pennsylvania. These cal" sounding as their earlier versions. GE 6SN7GTB (1960s). This tube was are still available from many NOS dealers. Another great sounding tube is the slightly more distorted that the GE Rating 87 Raytheon 6SN7WGTA (1950s vintage). 6SN7GTAs. It was less detailed and had

V A C U U M T U B E V A L L E Y IS S U E 11 V T V O C T A L L IN E S T A G E P RO J E C T

amp with VTV Octal Line Hammond 270BX some solid- 20 2x state power 1K, 2W 1K, 2W Stage Project amps, but 1/2A not all. Slo-Slow By Eric Barbour and (output filter capacitors Charles Kittleson A 5Y3GT on pre-amp schematic) tube rectifier 0 1999 All Rights Reserved is used in this design, After a dozen years of listening to (Figure 1), "peanut tube" preamps using or because tube 6DJ8s, I asked Eric Barbour to design a rectifiers add simple, good sounding octal-based pre- more "magic" amp. As many of you know, the reason and 3D to there are so many "peanut tube" preamps the music Si Junction Rect. (D1, D2 = 1N5401 is because these tubes are small and cheap. when com- or equiv 50V, 3A) — R1 = 4.70 5W By the way, so is their sonic performance. pared to typi- Schottky Rect. (D1, D2 = 1N5820 or 12SN7GT equiv 50V, SA) — R1 = 6.80 5W 22µF 2 x or Miniature dual triode tubes typically have cal cheap sili- 100V T 12SX7GT a small soundstage, tinny sound, are sub- con diodes. Figure I: Power Supply ject to microphonics and can be irritating With this to listen to. Short of using obsolete 56 or transformer, you could also use a 5V4G, The volume control is a Noble dual 76 triodes, we decided to use the venera- but do not use a 5U4, because the fila- 100K type. Performance was improved ble 6SN7, that can still be found for rea- ment current is too high. DC heater significantly when we installed a Gold sonable prices. The 6SN7 typically has a Point dual 100K stepped attenuator. larger soundstage and is super smooth. As Adding the Gold Point cleaned up the with all tube types, different brands and sound and reduced any mistracking of the batches can have noticeably different sonic channels. signatures. The beauty of this line stage is that you can experiment with the literally dozens of 6SN7 types to get exactly the sound you want.

We were not willing to use an ordinary aluminum box for the enclosure, so I con- tacted SpireAudio. (Note: Unfortunately., at press time. SpireAudio was out of busi- VTV Line Stage ness.) We used a 10x 17x2.5 inch alu- minum chassis that was powder coated power is derived using Schottky diodes. black. All input, output, power, fuse, and In order to keep hum to a minimum, switch holes were cut by SpireAudio. The copious amounts of filter capacitance were beefy solid aluminum knobs were needed to keep hum below the 1 millivolt This preamp is a super smooth sound- obtained from Ron Welborne. The result level. is a professional-looking instrument with ing unit and is very easy to listen to for lots of room inside for improvements and The power transformer is a Hammond extended periods without listener fatigue. upgrades in the future. 270BX (550V CT, 5V@2A and In fact, we listened to over 30 types of 6.3V@2A) which allows for a 370V plate 6SN7s with this unit and loved every The circuit design of this project is a voltage on the 6SN7s. Higher voltages minute. Overall, the VTV line stage is a classic cathode follower driven by a gain make the tube more linear and more preamp that you can live with for a very stage. Two 6SN7s are used, one per chan- "exciting" sounding. The power supply long time, perhaps a lifetime. nel. Overall gain of the line stage is about schematic, (Figure 1), also shows how to NOTE: High voltages are used in 12, which should be adequate for most wire this preamp for 12SN7s or 12SX7s if this project. Use caution and never applications. It is possible to use this pre- you desire. work on tube equipment when power is Figure 2 shows one side of the applied. VTV assumes no responsibility +370VDC line stage and indicates all com- if you do something careless or stupid while building or using this line stage. 6SN7GT/ ponent values. Note that the line 12SN7GT/ stage has switching for three Inputs 12SX7GT/ inputs. We used an old Dynaco etc. Input A special thanks to Fred Slaven at 0:440 v70aF ou put PAS-3 selector switch for this task, Selector 4 330µF but you can use a higher quality SpireAudio in Sacramento for assisting us 450V gold or silver contact switch. with the chassis used in this project. Also, 6 100K Coupling capacitors used are the dual audio thanks to John Atwood, VTV Tech Editor pot. Ultra-Tone Silver Foil in oil rated for fine-tuning the circuit. 330µF at 0.47uf @650V. These caps are 35V (ground to clear, deep and huge sounding. chassis here) (connect power Figure 2: Line Stage supply ground here)

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1 0 I N S I D E RICHARDSON E LECT RO NI CS

Richardson did not acquire the General Electric receiving tube facility in Inside Richardson Kentucky. We did, however, acquire the GE plant in Schenectady, New York, which made industrial tubes. The plant in Electronics Kentucky was purchased by its employees. That is when it became MPD, which An Interview stands for Microwave Products Division. By John Atwood and Charles Kittleson 1999 All Rights Reserved We became the sole source distributor for the GE receiving tube line, but we did not have anything to do with the acquisi- tion of that plant. The following is an interview with Dan transmitting tubes); ITT (which recently Erickson, Bob Birkeneder and Jerome became Triton); and GE (which became So they still exist as MPD? Czajkowski, Applications Engineers for MPD). Plus, we have the older brand Richardson Electronics, La Fox, Illinois names: RCA, Tung Sol, Philips, They still exist as MPD. They still pro- USA Raytheon, EEV, Thomson, and Western duce planar triode-type tubes, which are Electric. ceramic and metal tubes used in avionics When and how did Richardson Electronics and marine applications. We have also start operations? Richardson, I believe, in the past has pur- branched off into other things—like chased tube processing equip- The corporate history actually goes back ment from established tube to 1947 when Richardson first started out companies that have gotten as a replacement distributor of electron out of the business. Can you tubes, so the very basis of the company give us a notable example of was the vacuum tube. The first location this? was Wayne, Illinois, which is not too far from where we are now in La Fox. From Richardson purchased the Wayne we moved in closer to Chicago, equipment from RCA that and later we moved into Franklin Park. came from their small power tube division. That included What were some of the first products that tube types such as the 811A, Richardson produced? the 812A, 810, 845, 211, and a whole host of other Initially, we distributed vacuum tube ones. We primarily had products from a number of manufacturers started building those prod- back then. There were suppliers including ucts for our government GE, RCA, Amperex and Eimac. A whole contracts. We have also pur- host of tube manufacturers who we were chased a portion of GE's industrial prod- Breathalizers and radar guns and things distributing products for—either directly ucts, which included Ignitrons. We pur- like that. or indirectly. We acquired companies and chased part of Western Electric—primari- would also acquire brand names. So as we ly their cold cathode tube division. And When you look at the tube market, how do acquired National, we acquired the along with that, we obtained the equip- you decide whether to sell your own tubes or National brand, and as we acquired ment for some of their power grid tubes. to rely on outside suppliers? Cetron, we acquired the Cetron brand. We acquired Philips and Amperex prod- If there is an outside supplier already What are the current brands that you are uct lines, which were primarily power tetrodes and triodes, and some receiving producing the tube, we will approach selling now? tubes. Amperex was still building some them first. We prefer to be a distributor of We sell Eimac (which became CPI), receiving tubes when we took it over. the product. If there is no existing source Amperex, Burle (which was formerly RCA anywhere then typically we consider our- In addition, we acquired portions of the selves the manufacturer of last resort. , Raytheon Obviously, when you start something up Klystron division from scratch, there are a lot of variables and portions of that need to be taken into consideration the concerning: if the equipment is available; Westinghouse do we have engineers that can do that power grid divi- particular type; are there any drawings sion. Cetron had that are available from the past; all those also been pro- kind of things would affect the decision. ducing photo But basically, once we have determined tubes and some that, yes, we can build the tube, and no small power grid one else is building it, at that point we tubes, such as come up with an estimate for the cus- the 810. Cetron tomer indicating net cost per piece. was also building 845's, 300B's, Actually, that is one of the reasons we and so forth. got into producing tubes in the first place back when we bought National. We did

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11 I N S I D E R IC H A R D S O N E LE C T R O NI CS

that because most manufacturers of the various types, and now you are getting tomer, why not branch off into the con- industrial tubes were threatening to exit into the tube types most of your readers sumer market? the business and leave us without product wouldn't have any interest in at all—kly- to sell. That is when it was decided that strons, old magnetrons, hydrogen thrya- We set up an APD customer service we would go into building tubes to main- trons and things like that. It is the tube operations here in La Fox. APD employ- tain the market. Everybody thought that oddities that are coming out now. ees were picked for their ability for excel- by this time, the industrial market would lent customer service, because we knew decay. This was not the case and it is still Is the military still consuming good large they were going to get a lot of questions, not the case today. quantities of receiving tubes or has that probably more so than they would get on dropped oft? the commercial side. What percentage of tube sales are to (1) the military; (2) the hi-fi/audio market; (3) the To the best of our knowledge, they have We also needed applications engineering industrial market; (4) the broadcast market; dropped most consumption off altogether, that could answer more technical ques- and (5) other special applications? with the exception of maybe one or two tions. We now have four different engi- pieces of equipment in the military that neering staff that are involved in APD. If you look at all tube types, which are still using receiving tubes. They have would mean power tubes, receiving tubes, inventory for them and they are keeping One of the things that we have done is klystrons, you name it, that would fall that inventory. But we are only talking the re-introduction of the Amperex Bugle into the tube area, military sales would be about a couple of types that were basically Boy. With the acquisition of Amperex, we about .5%; the audio and guitar amp old TV-type tubes. acquired some of the equipment that was market would be 3%; used in the original manufacturing of industrial market, 36%; their receiving tubes. We now age audio broadcast market, 33%; types under full load for 24 hours on the and "other" markets, 27%. original Amperex aging equipment. Once "Other" markets includes they are aged, we perform the various tests medical, avionics and on them including a full harmonic distor- marine. Now if you look tion test. The Bugle Boy is a premium- just at the receiving tubes, grade tube, and a product that will be sta- it actually changes quite a ble, for one thing, and will hopefully be bit, because 54% of our pleasant to the ear when you plug it into sales actually is done in the equipment. With each tube, there is a the audio/hi-fi market; test certificate indicating individual per- industrial picks up 18%; formance measurements. broadcast drops all the Most of the original Bugle Boys were made way down to 3%; and our in Holland or other European countries. "other" markets will pick What is the country of origin for your new up 25%. So it really—if Bugle Boys? you can pinpoint which kind of tube we are talking about, it does We use Philips tubes, GE tubes and Switching gears here a little bit and getting make a difference. Depending on any other high-quality brands that we have in more into the area that many of our readers year, 51 percent of our receiving tube sales stock. are domestic and 49 percent are foreign. are interested in—the new Richardson Audio Products Division. Could you kind of One of the main things that VTV readers How did the recent military base closures give us an idea of what you are going to be ask us about is what the sound of the tube is affect Richardson and other companies like doing with that division—what kind of like. And even though it's a little hard to you? things we can expect? measure—some particular brands have had certain types of sound. If a customer buys a It was a blessing; and in some cases, it APD stands for Audio Product Division new Bugle Boy from Richardson, will we be was a nightmare. You had the government and that was really put together with the assured to get the same sound quality as the selling hundreds of thousands of tubes off understanding that this whole market of original Bugle Boy? and some of the vendors that bought that the audiophile was becoming more and product are now selling it at below market more important. Our focal point would That is a good question. We have a value. The types that were still being be directly to the consumer. This was large supply of tubes in inventory that made by China, Russia, Czechoslovakia, something that Richardson could become will remain constant for some years to those factories are going to see a reduction well-known through. We are a public based on the amount of inventory that company on the stock market, so the was sold off by the government; but that more references we could possibly get to remains to be seen. Richardson was going to help us. In addi- tion, we also had stockpiles of inventory Do you see this dumping of surplus tubes here of the tube types that your readers continuing in the future or do you think it and our customers would need. If we put is going to dry up? our heads together we could determine what audiophiles really need and a lot of We think it is pretty much done. It it is special one-to-one attention. This is seems like the decision was made to start really our first endeavor at the consumer this dump and they did volumes of market and because we started out as a dumping and now it is down to a trickle. tube business for the commercial cus- You will find maybe one or two lots of

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12 I N S I D E R IC H A R D S O N E LE C T R O NI CS

sons we stopped producing the KT88. We follow guidelines much like the mil- Unless we had an OEM that came to us itary, as far as their inspection process on and said, "Look, I want this and I want to product. buy x number rubes." I mean, it goes back to what we said earlier to determine How do you plan to cultivate the growing whether we are going to build a tube or public interest in tubes, audio amps, pro- not. We really can't keep production going audio, etc? on something that is very difficult to sell Obviously, one of the main ways is to because of the price. All of our tubes are advertise more. We are advertising in pub- put together by hand. We don't have any lications such as your own and others. We automated equipment producing tubes. will be at different trade shows. As you Do you still have a stock of the Richardson know, I think probably more than any- KT88? body, word of mouth in this particular market is so strong, that we are counting come. We measure the tubes with Hewlett We have sold the entire stock we had. on that, as well. Once we get some favor- Packard spectrum analyzers that are very able feelings out there from the customers Do you plan to reintroduce the 759IA? accurate. Once we've established a specifi- about how well we can serve their needs, that should help to play a part in how cation, we are not going to change it for a No, but we would consider distribution successful APD becomes. different manufacturer's tube. If their tube of the 7591A if another vendor produced doesn't make it, it doesn't make it, period. a quality product. Beside vacuum tubes, do you plan on getting We're not going to deviate from the speci- into other audio or hi-fi related products? fication just because we might have to Do you have plans to introduce any new change the supplier some time in the tubes or new designs, the way Svetlana did In the long term, yes. We have dis- future. with their SV8I 1 series? cussed several different products including tube dampeners, premium capacitors, Which tubes are you going to be introducing If we had somebody who came in and transformers, etc. But what products those in the Bugle Boy line? said, "I'll pay for developmental costs, and are and who the manufacturers of those I'll guarantee you an x-thousand produc- products will be has not been determined Initially we introduced the 6DJ8, 6922, tion run of these tubes," we would con- yet. 12AX7, 12AU7 and 12AT7 Bugle Boy sider doing that. But other than that, no. types. Later, we will bring in the EL34 We don't have any intentions on doing Where do you see the future of vacuum tubes and 6550A types as Bugle Boys. In addi- that. in audio going? Do you see it going as an tion, the new packaging looks better than indefinite thing or is it a just a passing fad? the original Amperex packaging. Plus, we Could you explain your tube matching and are using the original Bugle Boy logo on quality control process for audio tubes? I think tubes are reaching a far broader each tube. market, and they are now reaching the Somebody may call us and say they 20-something males. Often these are gui- need a pair of 12AX7As, for example, tar players already using tube guitar amps. and they are not looking to buy the Bugle Some of these people can afford to get Boy series. In that case, we would take into other types of tube gear. Also, there tubes without any aging, test them, and are new audio publications coming out match them for plate current, and that specifically dealing with vacuum tubes. In would be a matched pair. We do that with addition, the established audio publica- power grid tubes in the broadcast indus- tions are reviewing more and more tube try, as well. We do an incoming inspec- equipment, every month. So all indica- tion on all the product that we buy. We tions are showing that the market is grow- take a percentage sample from each ship- ing, and has been doing so since, I would ment, and run it through its paces to say, the late 80's. With more manufactur- make sure that it makes specification, ers coming out with lower-priced tube looks good and that there are no physical gear, and with speaker manufacturers defects to it. making speakers that really work quite well with tube amplifiers, I think the mar- What types of audio tube types will This may be a nitpicking point, but does that mean that you only do sample testing ket is really going to be on the upside for Richardson actually be manufacturing in- quite some time. house, if any, next year? on the lots, or does every tube go through at least a minimum test? The only ones that we are currently making is the 300B and the 845. We built the KT88 for McIntosh to use in their re-issue MC275 power amplifier. But we found that to continue production, you need a large audience to be purchasing these things. And, quite honestly, when you start getting up over one hundred dollars per tube, for a KT88, we find that people are very reluctant to spend that kind of money. So, that's one of the rea-

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13 M ID - P RI C E D V IN T A G E A U D I O

The following list includes desirable Mid-Priced Vintage mid-priced vintage audio items. By no means is this list exhaustive, but it includes equipment that is sonically satisfying, cos- Hi -Fi Equipment metically pleasing and has investment potential. While this equipment is some- what scarce, it can still be located using Acrosound through Leak the Internet, audio buy/sell publications and referrals. By Charles Kittleson © 1999 All Rights Reserved Acrosound UL-II Amp In VTV #9, I discussed budget priced If you plan to use any of the equipment The 60 watt Acrosound UL-II tube hi-fi components under $350. This listed in this article, thorough repair and Ultralinear amp came out in 1957 as time we will examine mid-priced compo- restoration will be required. Tube ampli- either a kit ($79.95) or assembled nents in the $351 to $1,000 (1999) fiers have simple circuits and are normally ($109.95). Herb Keroes, designer of the range. These components are a bit more easy to restore, but tuners and preamps Ultra-Linear Acrosound transformers, difficult to locate than the budget units are more challenging. Best performance decided to get into the audio kit game due to their lower production figures and results will be achieved by locating an with the UL-II and subsequent amplifier collectability. Cosmetic and electrical con- experienced and reliable tube hi-fi techni- and preamplifier products. The UL-II was dition is a major consideration if you plan cian locally or through the mail to per- a very attractive audio artifact featuring to collect them for investment purposes. form vintage tuner and receiver restora- huge potted transformers on either side of For some reason, mint vintage hi-fi does tion. Or, if you have the electrical and the two-tone metallic brown chassis that not have a huge price differential from mechanical ability, conduct the restoration included a tube cage in the center. The equipment that is in average condition. yourself. It is a must to obtain a schemat- UL-II featured the famous TO-600 out- This is not true with other collectibles like ic and/or service manual beforehand. put transformer and a potted power trans- guitars; for example, with an average con- former. Most of the electronics and all of dition 1961 Fender Stratocaster selling for Restoration of tube gear includes: the tubes were mounted on a circuit $2,000-3,000 and a mint one selling for cleaning and dusting of the unit, cleaning board. This board was a weak point of $20,000+. and lubricating of switches and connec- these amps, because it got brittle from tors, testing and possible replacement of heat and age, causing the traces to lift I have been a serious collector of vintage tubes, replacement of old paper and wax from the board. Be sure to carefully hi-fi for over 10 years, and I know that for capacitors (especially in high-voltage and inspect the circuit board for damage every 50 average condition units of a par- coupling circuits) with good-sounding before purchasing this amp. Another ticular type, only one or two will be film types, replacement of selenium bias, weak point of the UL-II was the power found in mint condition. In the future, B+ and filament rectifiers with silicon or transformer. For some reason, they chose vintage hi-fi in primo condition will have FRED diodes, testing and replacement of to include the filter choke with the power much higher collector value because gear electrolytic bias, filament, B+, etc. capaci- transformer in the potted enclosure. The in that condition is very scarce. Many of tors, checking all resistors for any drift, transformer can fail from age, extended the items listed for in this article are replacing resistors in the phase inverter use or shorted filter capacitors. Tube com- already hard to find, especially mono with new close tolerance units, checking plement includes: 12AX7, 12AU7, two power amplifiers in pairs. If you find one, all important circuit voltages, and setting EL34s and a 5AR4. The amp can be re- it may take you a while to find its mate DC bias and balance. Tuners and biased to accept 6550s if the user desires. and you may have to pay more than you receivers may require tuner alignments The sound quality of the ULIIs is excep- did for the first one. and possible replacement of IF cans, coils tional. Measured frequency response was and other RF parts. 5 to 100,000 Hz + or - 1 dB. The music When buying vintage audio gear strictly presentation is smooth and rich with live- for investment and not for listening pur- When the restoration is complete, you sounding midrange. The sound is bal- poses, it is generally best to not replace will have an attractive, good-sounding and anced throughout the entire frequency older capacitors, rectifiers, resistors, etc. unique audio artifact to display and listen range. Some vintage amps in this power with new parts. True collectors will pay to. Remember that amplifier power rat- range can have boomy or loose bass, but the most for totally stock, original pieces. ings in excess of 50-60 watts are rare in the Acro is pretty tight. There is a vari- the vintage hi-fi world. If your able control on the amp that adjusts the speakers are satisfied with 30 to 60 damping factor from .5 to 10. According watts, you will find some extremely to many vintage audio enthusiasts, this is good sounding amplifiers in this one of the best sounding 50 watt mono article. Don't forget that 60 watts amps of the era. Finding ULIIs in pairs of tube power will sound a lot and in good condition can be difficult. louder than 60 watts of solid-state The cheap circuit board, as well as the power. Several of the items listed power transformer (which is prone to fail- here are more musical and pleasant ure), can be challenging. to listen to than newly manufac- tured gear costing many multiples Dynaco Mark III of the cost paid for vintage gear. An advantage for purchasing and Probably the most common vintage restoring vintage gear is that it typi- mono tube hi-fi amp ever produced in the cally appreciates with age. United States, the Ultralinear Mark III is Acrosound UL-11 (1958) still easy to locate. The Mark III was

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quality components and circuit design required less feedback and produced less distortion. Each 35 watt channel of the amp used a direct-coupled voltage amplifier stage driving the cathode-coupled phase inverter coupled to the Ultralinear, self-biased output stage. The power supply is a volt- age doubler using silicon diodes, a current-limiting surgistor and Dynaco Mark III ample filter capacitance. A plus is that the entire amp is point-to- introduced in 1957 and initially sold as a point wired, allowing for easy kit for $69.95! Producing 60 watts of upgrading and modifications. Good upgrades include replacing power and featuring the excellent A431 EICO HF 50 and HF60 Dynaco Ultralinear output transformer, coupling and bypass caps, replacing power Both the classic EICO mono HF50 this amp was an immediate sensation. It supply diodes with low-noise FREDs and and HF60 amps use the Mullard-type was the successor to the Dynaco Mark II, replacing resistors in the phase inverter and an EL34 push-pull amplifier that was first audio stage plate resistors with 1% front-end circuit. A single low-noise Dynaco's first product, introduced in precision units. EF86 was direct-coupled to a 6SN7GT 1955. The Mark II only had output taps cathode-coupled phase inverter driving for 8 and 16 ohm speakers, while the This amp is solid sounding and an alter- push-pull EL34s in Ultralinear mode Mark III added a 4 ohm tap. The chassis native to the Dynaco Stereo 70. In fact, I operating in fixed-bias. The rectifier was was nickel-plated and featured a gray- would rather listen to an HF 87 than any the slow-warmup, indirectly heated cath- brown cage that covered the entire amp. stock Stereo 70. Sound is clear, and pow- ode 5AR4/GZ34. The circuit was Apparently, Mark Ms were produced until erful, but still has detail and transmits the designed with 21dB of inverse feedback the late 1970s. This was the first popular musical energy. Published frequency and a damping factor of 12 or more. tube amp in America to use the Genalex response was measured at 5 to 100,000 Hz + or - .5 dB. Hum level was 90 dB below These amps were similar in many ways KT88. Modern 6550s can also be used with the exception of the output trans- with no modifications. The front-end cir- full output. Many modern tube amplifiers cuit was on a single-sided printed circuit would not be able to meet these specs. board and used a triode-pentode 6AN8. With 35 watts RMS per channel, the The rectifier was the slow-warmup 5AR4. HF87 will effectively drive most home audio speakers with ease. Note that the There were dozens of mods and matching preamps for EICO tube stereo upgrades developed for the Mark III. amps were their HF85 and ST84 models. Many of these were published in Audio Amateur Magazine and other related EICO HF89 publications. Several companies currently offer upgrade driver stage and power sup- Also available in kit or assembled ver- sions, this 50-55 watt per channel stereo ply modification kits as well. No specific recommendations can be given for any of amp is one to look for. It is another these mods or upgrades, so it will be best "sleeper" amp with huge output transform- to ask around. ers (that according to John Atwood, VTV Technical Editor, have outstanding low fre- In stock form, the Mark III is a power- quency response). Bruce Tilden, a local former. A super high-quality potted ful sounding amp, but with super-efficient transformer expert, claims that the HF89 Chicago transformer was used on the speaker systems, the bass may seem a bit output transformers go down to 4 Hz! HF50. This transformer has great high- flabby and the mids a little hard sounding. Apparently, they were sourced to a vendor frequency response + or - .5 dB from 6 Replacing the coupling and electrolytic other than Stancor or Chicago, whom Hz to 60 Khz. capacitors can improve the sound, though. EICO used for most of their iron. This amp was initially designed to be used On the HF60, an Acrosound TO-330 with the low efficiency new acoustic sus- The circuit is similar to the HF87 above, output transformer, was standard for a pension speakers such as those produced but the output tubes operate in fixed-bias slightly higher cost. The frequency by AR and KLH in the late 1950s. mode and the B+ voltage is slightly higher. response of this transformer was an out- Therefore, I would not recommend using This amp is truly one of the best vintage standing + or - .5 dB from 5 to 100,000 the stock Mark III with super-efficient and tube stereo units, with a balanced sound Hz. HF5Os and HF6Os are getting hard horn-type speakers. throughout the music spectrum. Bass to find, but are both great vintage power response is nothing short of spectacular, amps. The HF50 has a tilt towards the EICO HF87 with muds and highs that are sweet and high frequency range and sounds more detailed. Upgrades and mods are similar to extended than the HF60 which has a The HF 87 was available in kit ($74.95) the HF87 listed above. The HF89 was great bass response, but in stock form is a or assembled ($114.95) form from 1959 made in fewer numbers than the HF87 little darker sounding than the HF50. through 1965 or so. This was a beefy unit and will be somewhat more difficult to Both amps can be easily modified, by with an excellent front-end design using a locate. connecting the EF86 in triode mode, single 12AX7 and two 6SN7GTs. High-

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connecting the EL34s in triode, beefing sounding with a good deal of preamplifier. Using high-quality NOS up the power supply and replacing the high-frequency detail and quickness. Bass tubes is also essential when using a 400CX selenium rectifier with a fast recovery response is powerful, mids and highs are in your system. When these preamps are diode. detailed, but not to the point of irritation. upgraded, the sound is lush and rich. The sound is close to a Marantz 8B Note that the earlier Fisher 400 stereo Fisher SA300 amplifier at a fraction of the price. preamp is also a good performer, but can This was Fisher's first mid-power stereo Another great-sounding amplifier from sound veiled unless completely rebuilt amplifier. It was introduced in 1960 and with new components, was made for about three years. It was especially signal path capac- called a "laboratory amplifier" because it itors and resistors. featured full adjustment of bias, DC and AC balance and AC hum. The amp used Fisher FM200B push-pull EL34 tubes with an all triode One step below the front-end (12AX7 and 12AU7) and dual famous FM 1000, the FM GZ34 rectifiers. Rated power was 30 200B is an extremely sensi- watts per channel RMS, but it actually tive and selective FM stereo put out closer to 37-38 watts per channel. tuner. Fisher produced Its power supply was very beefy and fea- more good sounding tube tured a huge power transformer and tuners than any manufac- Fisher FM200B ample filter capacitance. A later version, turer in the world during the SA300B, had slightly different circuit- the early to mid-1960s. ry, but the same tube compliment. the same era is the push-pull EL84 Fisher When Fisher and Scott tuners are com- SA100 basic amplifier. The SA100 is sim- pared with each other, most listeners pre- Modifications and upgrades include ilar in styling, but produces less power. fer the Fisher. Fisher FM has a rich, sweet detail that is fuller sounding than most Fisher 400CXII Scott tuners, which tend to have a thinner A perfect match for the sound. SA300, the 400CXII is a full- featured tube stereo preamp. The 200B uses a dual Nuvistor front- Preceded by the 400 preamp, end and has five IF stages. Dual 12AT7s the 400CX has more tubes are used for the cathode-follower output. and more features. There Most of the other tubes are common were at least three versions of tuner types that are easy to obtain. The the 400CX with the last ver- front-end tubes in tuners are run hard and sion called the 400CXII. Do should be frequently checked. The other not confuse this with the ear- tuner tubes have an average lifetime. As lier 400 preamp that was with most tuners, proper alignment is key Fisher 400CXII introduced in 1960. The ear- to the best performance. liest version has oval shaped replacing all coupling and bypass capaci- selector buttons and a lacquered brass Fisher R-200 tors, replacing low-voltage electrolytics faceplate. Later versions had a brushed The R-200 is basically an FM100B with and bias caps, checking and replacing aluminum faceplate with round selector a very sensitive AM section. Although the phase inverter plate and grid resistors with buttons. R-200 does not have a Nuvistor front- 1% metal film units. It is best to obtain a end, it is still a very sensitive and good factory schematic and service manual for A weakness of the 400CX is its com- sounding unit. Some experts consider the the correct bias, AC and DC balance pro- plexity with a plethora of switches and R-200 a better-sounding tuner than the cedures. controls. Regularly cleaning the switches, FM200B. If you listen to AM radio talk connectors and tube sockets can make a shows or sports Compared to many push-pull dramatic difference in the sound of this E134 amps, the SA300 is very modern

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m m m m m ait CO M f•tiN P3P.. Citation II _Citation V coverage, the R-200 may be your ideal rectifiers and a driver choke design. A match to the Citation I, the Citation tuner. High-quality potted transformers were II was a beefy, high-performance power produced by Freed Transformer amplifier that was an exceptional per- Fisher FM1000 Tuner Corporation. 50A amplifiers are very former. This 120 watt amplifier used sweet and mellow sounding and work push-pull KT88s in Ultralinear mode. The FM1000 and its rack mounted well with horn loudspeakers. Later Fisher Massive, potted output transformers version, the FMR-1, were the finest FM monoblocks not pictured include: the made for HK by Magnetic Windings stereo tube tuners ever produced by 55AZ with push-pull 6550s (and later Corporation of Easton, Pennsylvania, Fisher. This legendary performer had six EL34s), the 70AZ with push-pull 5881s, were stable to frequency extremes beyond IF stages, two meters, extensive controls the 80AZ with push-pull EL37s, while 200kHz. A high-capacity power supply and a cathode-follower output. The the Fisher 100 was basically an 80AZ using silicon diodes and a voltage doubler FM1000 is super sensitive and is very life- with different cosmetics and the Fisher was used with the potted power trans- like sounding, especially if carefully ser- 200 used push-pull EL34s (note: the former. The Citation II was a controver- viced and aligned. Fisher also produced a Fisher 90AZ and 125AX will be featured sial design in that it used three feedback rack version called the FM1000R, used in later articles on Fisher). All of these loops to obtain super low distortion. by FM radio stations for monitoring and amps are beautifully made, sonically satis- re-broadcasting. fying and are worth picking up. This amp features a voltage doubler 450V power supply that is very similar in Fisher X1000 Integrated amp Generally, they need restoration work including new capacitors, diodes, tubes, design to the Citation V and Lafayette This beautiful device was Fisher's largest etc. Occasionally, you will find an amp 550 power amplifiers. Some enthusiasts tube integrated amp. Using push-pull that has a blown driver choke and this sit- did not like the sound of the all pentode EL34s, it produced 55 watts RIVIS per uation can be challenging. front-end and consequently changed the channel! The X1000 was the most pow- driver tubes to triodes. In addition, many erful tube stereo integrated amp during Harman-Kardon Citation Series (tube Citation IIs were scrapped for the super high-quality output transformers by cus- the 1960s. Output transformers were type) huge and the amp weighed in at almost tom tube amp builders during the 1980s. The Harman-Kardon Citation I thru V 50 pounds. The X1000 was full-featured Series tube audio line were introduced in The high power output and super-wide and featured a center channel volume the late 1950s and sold through the mid- frequency response enabled the Citation control as well as a control for the Fisher 1960s. They were offered either as kits or II to drive most loudspeakers. (For more Space Expander reverb system. Not only fully assembled and tested. The Citation detailed information on the Citation I is the X1000 large, it is probably the best Series were attractive and had the massive and II, see VTV issue #4.) There a few sounding high-powered tube integrated styling of the early 1960s including critics of the Citation II amp who amp ever produced. There are two ver- turned aluminum knobs, champagne claimed it "gave them a headache after sions of the X1000. The first version had faceplates and thick cadmium-plated steel extended listening." brown bakelite knobs with no brass cap. chassis. The second version of the X1000 had the Citation produced a high-quality FM new brass medallion knobs and a head- The Citation I was a full-featured pre- mono tuner, the Citation III and later, phone jack was added. amp with an unbelievable array of con- the Citation IIIX (stereo multiplex ver- trols and features. Some enthusiasts feel sion). HK claimed in their literature that Fisher Mono Power Amplifiers that this was one of the best vintage tube the III was the world's most sensitive During the 1950s, Fisher produced sever- preamps ever made. Others think it is tuner (0.65 microvolts for 20 dB of quiet- al great-sounding tube mono-block overly complicated and has too many ing). The front-end utilized a Nuvistor, amplifiers. All of these amps used ultra- stages. The circuit topology is anode-fol- there were three IF stages followed by a high quality potted output and power lower based, which can improve low fre- wide band Foster-Seely discriminator, two transformers for noise reduction and cos- quency response. The preamp has 18 tuning meters, two gated-beam limiters to metic reasons. The first of their compo- stages of gain and utilizes nine dual-triode ensure exceptionally high capture ratio nent amplifiers was the 50A (pictured) tubes. The design used passive equaliza- and lower distortion. The Citation III and the later 50AZ that featured variable tion in the phono stage that required an had a special design wide band audio cir- speaker damping. The 50A was a 40 watt additional gain stage. cuit for extended frequency response and triode-connected 6L6 amplifier with dual ‘'unmeasureable" phase shift. Many tuner

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appear to have been manufac- tured by another ven- 'k..S U L LC ;Imo dor. They are thought to have a slightly hazy sound and lack of transparency Ileathkit SP-2 when com- pared to the enthusiasts claim that a properly restored Citation II and aligned Citation IIIX is their favorite transformers. The Citation V tuner in terms of sensitivity, separation and is one of the easiest amps to audio performance. However, the Citation modify to full triode input IIIX multiplex unit is questionable and a (replacing the pentode (12BY7) nightmare to work on. An external multi- with a triode (a 12AX7 does plex adapter is recommended. wonders). The triode input converted design that was used in at least two of Citation Vs are real contenders. And Knight's integrated amplifier designs. A little later in the Citation series run, since the power supply voltages, etc. are The KP-50 unit has two phono inputs HK introduced the Citation IV stereo- essentially identical, this circuit works with some rather unique switching. One phonic control center. The IV was a well with the Citation II. With this mod- phono is a conventional RIAA stereo compact and less complicated preamp ification, the amp sounds extremely trans- input and the other is a mono only and compared to its older brother, the parent. Citation I. The preamp was full-featured, has selected jacks for specific old phono cartridges (GE, Pickering, etc.). When but only used six dual triode tubes with Heathkit SP-2 an anode follower output. It had separate the selector is in this position it also acti- tone controls that were able to be Heathkit's deluxe stereo preamp was the vated various old record equalization switched out of circuit as well as a vari- SP-2. It was a modular unit where you curves. able blend control for the center channel could start out with one channel and the Lafayette KT600A output. Note that when the tone control power supply, then upgrade to stereo, by was switched out, absolute phase was buying the other channel. The SP-2 had According to many enthusiasts, the changed. HK used DC on all heaters as typical styling of the late 1950s with a KT600A preamp is the best sounding vin- well as low noise metal film resistors in black faceplate, brass insert knurled knobs tage tube stereo preamp. Designed by Ed critical places to reduce thermal agitation and a black and gold-swirl case. Most Duda, former Lafayette Electronics and hum. Many vintage hi-fi enthusiasts components were mounted on a circuit designer, and Stuart Hegeman of claim that the Citation IV is a better board and each channel featured two dual Harman-Kardon Citation fame, the sounding, more musical preamp than the triodes and an EF86 pentode. A unique, KT600A was available in either kit or Citation I. but frequently lost accessory was the assembled form. The circuit used eight remote stereo balance control on a long 12AX7s and a selenium rectifier stack. The Citation IV has a tiny outboard cable. The matching Heathkit amp is the The preamp uses an anode follower topol- power transformer mounted on the back AA-40 ogy for the line-out to the amplifier. This of the unit that almost looks like an after- may be one of the reasons the KT600A thought. Apparently, relatively poor qual- Knight KB-85 Amplifier sounds so good. Apparently, Stu ity parts were used. Use caution when During the late 1950s and early 1960s, Hegeman did not like the sound of cath- upgrading the Citation IV. Try not to use Allied radio produced some great sound- ode followers. A similar concept can be too many metal film resistors. Also be ing tube hi-fi gear for bargain prices. seen in the Harman-Kardon Citation I sure to replace the electrolytic output caps One of these amplifiers was the KB-85, a and V preamps. with modern film types. 60 watt tube stereo amplifier on a chrome chassis. The amp featured ultra-wide Most of the components in the KT600 Citation V was the last of the Citation response potted Chicago transformers and are mounted on a beefy, thick circuit tube hi-fi line and was an excellent per- push-pull Mullard EL-37 output tubes. board. Power supply and filtering capaci- former. This 80 watt stereo amplifier had The front-end was a Mullard design using tance is very ample. In some KT600s, a simpler circuit than the Citation II and an EF86 and a 12AX7 for each side. the power transformer can exhibit a slight featured the newly introduced GE 7581 There were also dual 5AR4 rectifiers and buzz. Some enthusiasts fixed this prob- type which was an uprated 6L6GC. The a massive power transformer. lem by building a separate power supply. circuit featured only one feedback loop Like most preamps of this era, plastic- with a single 12BY7 and a single 6CG7 in Knight KP-50 Tube Preamp cased paper capacitors are used. In most the front-end driving the output tubes in This was a very unique stereo preamp cases, these capacitors should be replaced straight pentode mode through super high offered in kit and assembled versions. It for the most sonic detail. In addition, the quality output transformers designed with used 12AY7s in the phono stage and selenium rectifiers for B+ and filament resonant frequencies above 200kHz. 12AU7s in the gain and output stages. A voltage must be replaced because they It has been rumored that the Citation V modular circuit board construction makes develop a high series resistance with age. was not designed by Stu Hegeman. The this unit a bit of a bear to work on. This This condition lowers the voltage and output transformers are not potted and unit essentially fleshed out the preamp produces excessive heat in the rectifier.

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Lafayette KT550 Amplifier have switchable taps for varying line volt- through 1957 and there are several varia- ages and speaker impedances. tions. When first introduced, many This design was completed by Ed Duda TL/12s were sold to national broadcasting with some involvement by Stu Hegeman. Sound quality is balanced, rich and organizations around the world to be used In a weird way, the design philosophy musical. The ST20 represents the epitome as monitor amps in stations and studios. combines the multiple feedback wide of British EL84 sound. These amps are band design of the Citation II with the easy to upgrade because 90% of the parts This amp uses terminal board construc- output stage of the Citation V. The 550 are mounted on the sub-chassis turret tion and is also beautifully made. The was designed prior to Hegeman going to board. Sonics can be improved by re-cap- sound of the TL/12 is rich, detailed and work for Harman-Kardon. According to ping and checking/replacing key resistors. very warm. It is extremely musical and a recent conversation with Ed Duda, It is best not to modify these highly col- easy to listen to for extended periods. A Hegeman left in the middle of the project lectable units. later version of this amp, made from and the design was completed by Duda. 1956-57, was the Leak TL/12 Plus that Some feel that the 550 was a prototype used push-pull EL84s. These are very for the later Citation II design. sweet sounding amplifiers and sought after by British amplifier enthusiasts seek- It is a standard pentode design using ing lower powered amplifiers. Acrosound transformers and was original- ly intended to use 6550s, but for cost rea- Leak TL50+ sons, the design was changed to accept An extremely rare amp, the TL50+ the newer RCA 7027As. The 550 uses monoblock was only made during 1956- 6CL6 pentodes in the input stage and a 58. Output power is 50 watts derived 6BR8A in what is probably the strangest from push-pull KT88s. Front-end tubes phase inverter on the planet. As men- are EF86 and 12AX7 with a 5AR4 rectifi- tioned earlier, the power supply is essen- er tube. This is a great-sounding higher Leak ST60 tially identical to the Citation II. powered amp and will drive most avail- Sonically, some consider the KT550 able speakers. TL/50+s are very hard to Leak ST50 and ST60 amplifier to be much warmer and more find in pairs, but singles should still be dimensional than the Citation II, albeit The big brother of the ST20 is the picked up because you can always find with a slight amount of grain. This unit ultra-linear ST50 (1958-63) ($189.00) someone who is looking for one to match his. Leak also produced the TL25 and also lends itself to the triode input/driver that uses EL34s. Power output is about modification mentioned above (see 25 watts per channel. Leak specifies that the TL25+ using either push-pull KT66s Citation V). The output stage can be you can use either EL34s, KT66s or or EL34s for 25 watts of power. made to accept almost any output tube 5881s in this amp. Each of these tubes from 6L6/KT66, EL34 to 6550/KT88 will give a different sonic signature. Summary tubes. Other tubes are similar to the ST20 men- In this article we examined several mid- tioned above. Cosmetically, this attractive priced but great sounding amplifiers, amp has the same gold lacquer finish as tuners and preamplifiers. It was not pos- other Leak products. With the ST60 dur- sible to list every one in this category, but ing 1962 through the mid-1960s, Leak we did cover the more well-known ones upgraded the power of the ST50 to 30 with higher production figures. In our watts per channel by increasing the B+ next segment of this article, we will exam- voltage. They also abandoned the metal- ine the remainder of mid-priced vintage lic gold finish with the ST60 (also ultra- hi-fi gear from McIntosh to Scott, etc. linear) (1964-67) and finished it in dark maroon. A special thanks to Al Pugliesi (The Fisher Doctor) of Staten Island, New York and Construction quality is the same as the Roger Coon of Redwood City, Califbrnia for ST20 and very easy to upgrade. The their assistance with this article. matching preamp for the Leak stereo amps is the Leak Point One Preamp. A very "60s" looking piece with an engraved Leak ST20 and back-color filled plexiglass faceplate Throughout the 1950s until the mid- this is the perfect match to the other Leak 1960s, Leak produced some of the most products. The Point One used four EF86 attractive, finest built and excellent tubes and was powered by plugging it Next time in VTV: sounding equipment available. The ultra- into one of the Leak amps. linear ST20 (1958-67) combines two -2A3 Filamentary Triodes Leak TL12+ amps on one chassis. This Leak TL/12 10 watt per channel amp uses push-pull -Scott EL84 Amplifiers Originally called the Leak "Point One" EL84s, three 12AX7s and a 5AR4 rectifi- Amplifier, the Leak TL-12 is one of the -PP 300B Amplifier er. Most of the circuit components are best-sounding vintage amps I have ever mounted on military-style turret boards -Bookshelf Speaker heard. It produces 12 watts from push- and the wiring quality is beautiful. Not pull KT66s that are triode-connected and to mention the deep metallic gold lacquer Shootout!!! drive a massive open-frame output trans- finish on the chassis and transformers. former. The TL/12 was made from 1949 -300 Watt Triode Amp Both the output and power transformers

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which occupied a great deal of space. COMPUTING WITH TUBES: Overall, it was akin to a crippled Motorola 68000 in its basic layout-occu- THE SAVAGE ART pying 3100 square feet. The number of "firsts" that Whirlwind 5: THE FIRST REALTIAIE MACHINE can claim is considerable. Since it was the By Eric Barbour 0 1999 first digital computer to get an analog-to- digital converter, it was the first to be used in real-time data acquisition. And it was the first computer to be capable of In 1944, the U.S. Navy's Bureau of Barta Building, starting with first layout generating real-time graphics on its 14" Aeronautics wanted to design a better in August 1947. CRT display, which could be modified flight simulator to help train pilots more with a handheld "light gun". When the quickly. Because the war was demanding The ONR was very unhappy by 1948. Williams tubes were abandoned, ever-more experienced pilots, and training Their own Mathematics Branch warned Whirlwind became a pioneer of core them with the primitive equipment of the that the MIT team was not sufficiently memory in 1953. A small computer, period was slow and expensive, the Navy experienced in advanced mathematics. called the Lincoln Memory Tester, was hoped that an electronic system could Yes, at the time, Boolean algebra and built to exercise the core module. This provide realistic flight controls in a simu- binary arithmetic were regarded as tester was built by some MIT students lator. extremely complex and obscure fields of study. And Forrester's team did receive who went on to found Digital Equipment The Bureau's Special Devices Division, remarkable freedom during the design and Corporation. led by Capt. Luis de Florez, let a very spe- construction phase. The enormous assis- More significant, Whirlwind was so suc- cial contract to MIT's Servomechanisms tance they received from Sylvania was a cessful that it led to the formation of Laboratory. Director Gordon Brown and big help. MIT's Lincoln Laboratory. Which, in liaison officer Nathaniel Sage recruited turn, used Whirlwind's basic design as the two young men to oversee the project-- One thing that Sylvania got out of the kernel of the biggest, most expensive and Robert Everett, and a brash fellow named Whirlwind project was priceless. The most complex electronic computer system Jay Forrester. engineers were trying to use 7AD7 radio pentodes in the logic circuits. every built. That Cold War monstrosity, a At the time, the Bureau had a penchant Unfortunately, these tubes died very major user of computing tubes in the for naming its major projects after various quickly, because their cathode current was 1960s, will be discussed in the next cut off much of the time. Sylvania engi- installment. neers discovered the cause: impurities in the nickel cathode tubing. Ordinary radio circuits didn't see this, because the tube conducted some current all the time. For digital use, though, a special high-purity cathode was developed. Thus was born the 7AK7 pentode, the first electronic device ever developed specifically for digi- tal logic applications.

1948 was a turning point. The ONR was now balking at the endless requests from the Whirlwind team for more and kinds of atmospheric disturbances. So, more money. And there were endless tech- they called their most major project nical difficulties with the special Williams Whirlwind. Prophetically, as it grew and memory tubes being fabricated in MIT's grew, and threatened to entirely sweep own glassblowing shop. These complex away the Bureau of Aeronautics. tubes each had two electron guns, one for writing and the other for reading. Each As soon as work started on the simula- tube cost more than $1000, in 1950s dol- References: tor (called ASCA), Forrester started to lars. And Whirlwind needed 16 at first, 1. Project Whirlwind: The History of A work on the managers. He felt that limit- for 256 words of memory. Eventually the Pioneer Computer, Kent C. Redmond ing the machine to operation of a flight memory was expanded to 2048 words. and Thomas M. Smith, Digital simulator was not a good idea--why not The project might have died then, if Equipment Corp. Press, 1980. make it a general-purpose computing Forrester and Smith had not managed to machine? Then, not only can it operate a arrange some further support from the Many thanks to the staff of the Computer simulator, it can process radar data, calcu- U. S. Air Force. So, they eventually got Museum History Center and to Les Earnest late trajectories, and do many other jobs enough money to get the machine run- of Stanford University for their assistance for the Navy. Eventually, Forrester's push- ning programs by early 1950. with research. The Computer Museum is the ing shifted the focus of the project. And, unfortunately, its cost grew. As the war Whirlwind was a 16-bit machine, the current owner of the remains of Whirlwind. ended, and the Bureau became the Office first to have a word length based on a fac- of Naval Research in 1946. And as the tor of 8 (which is standard practice beast occupied a very large room in MIT's today). It had a hardware multiplier,

V AC U U M T UBE V ALLE Y ISSUE 11

20 T U B E D U M P S T E R 6 6 8 8 / 7 7 8 8

Uncle Eric's Tube 6688/E1 80F Output Input Dumpster F — © )' 0.47µF The 6688/E180F 200V 1000 = ,

100K 100H audio 1,3 T 47K taper

100µF + 25V 2200 Figure 1 Experimental 6688 For obvious reasons, the hard core of All resistors +150VDC line stage circuit tube DIYers has started to use high- are 1/2W (3mA) transconductance frame grid tubes for small-signal gain. Although they can vary in linearity, just as more conventional Of course, Philips wanted a piece of this put transformer for the choke, you can small-signal types do, frame grids offer low business, so they introduced the E180F in build a stereo preamp with this circuit for plate resistance and (hopefully) lower 1956. Unfortunately, they put a different less than $50. microphony. pinout on it, then had to promote it for Yet again, we see iron tradition in the NEW designs. Still, both relatively staid world of the SE amp. The in Europe and in the tendency has been to chase after the high- American Amperex form est Gm devices (and only glass ones at 6688, it got sockets in a that), which makes them scarce and variety of military and expensive. The current fad for the 417A civilian radio equipment. and 437A triodes and 7788 pentode, not Five years later came to mention recent demand for the obscure the 7788/E810F, also Russian 6C15 pentode, are driven by DIY introduced by Philips. peer pressure and conformity. And those The obscure 7788 was a particular tubes always were expensive; VERY tough tube to now that they are out of production, their manufacture. It repre- prices are skyrocketing. Meanwhile, very sented the outer limits of WE 404A, Mullard E180F, Amperex JEP 5847 and Amperex PQ 6688 good tubes languish in great piles in ware- glass-tube capabilities, houses. with its Gm of 50,000, and it was never as Dealers are charging up to $350 apiece for high-Gm triodes like the 437A, and One of the first widely used as 6688s due to its high price. about $100 for 7788s. Yet those same frame-grid pentodes So you can bet that we will never see dealers are stuck with mountains of 1980s was the Western 7788s made, ever again. surplus 6688s, which nobody wants Electric 404A Before you say "so what," bear this in because they don't have the highest Gm (1948). Widely mind: Getting such a high Gm means that ratings in the tube manuals. So, don't fall used in telephone you must have the grid VERY close to the for "Tube Manual Snobbery." Great sound microwave-multi- cathode. In this case, less than 1000 can be gotten from the 7788's smaller plex equipment, it microns away—much less than the thick- brother, at peanut prices. Yes, even though became an impor- ness of this sheet of paper. This a tough it is a pentode, and even in spite of its tant device for IF amplification. It occu- feat to achieve in a planar triode... and moderate transconductance. High Gm is pied little space, making it suitable for unimaginable in a conventional glass pen- NOT a magic pathway to nirvana. mobile radios. As made by other manufac- tode! Eindhoven's reject rate on the 7788 turers, it was known by its ETA number production line must have been astronom- 5847. ical. 6688 Specifications Our tests have shown a high Heater Voltage 6.3V degree of linearity in a typical 6688—on a par with 6DJ8s and Heater Current 0.03 amp 6922s. Yes, even though it is a Max Plate B+ 210V max pentode. Max Plate Diss. 3.0 watts max Figure 1 is a suggested experi- Plate Resistance 0.09 megohm mental circuit for a super-high- Transconductance 16,500 micromhos performance line stage using the Grid No.2 Volts 175 max 6688. You may have to do a little tweaking on your own with this Grid No. 2 Diss 0.9 watt max design to get maximum perfor- Grid No. 1 -Bias -50V max mance. If you use the primary of Cathode Current 25 mA max an old push-pull EL84 amp's out- Amperex 6688 Types

V AC U U M T UBE V ALLEY ISSUE 1 1

21 A S U S A A - 4 A M P L I F I E R K I T

the unit was powered up. Wiring of one of the bias electrolytic capacitors was correct ASUSA A-4 Amplifier in the schematic, but incorrect in the assembly instructions. This caused a VTV Kit Review reversal in polarity so that one of the bias capacitors failed. We had to replace that cap and wire it correctly. Wiring for the By Charles Kittleson © 1999 All Rights Reserved bias adjustment pots for one channel of the amp was reversed when compared to the other channel. One of the more prolific producers of initial power-up and bias adjustments, tube audio kits today is ASUSA of Seattle, performance test procedure, troubleshoot- For an experienced kit builder, this pro- Washington. Recently, they introduced a ing guide, parts list, schematic diagram ject should take about 16-20 hours. For a line of USA-made kits featuring point-to- and mechanical assembly diagram. rank beginner, about 30 hours may be point wiring, high-quality powder coated required due to some potential confusion steel chassis and beefy, US made trans- How Did it Go Together? in the assembly and wiring instructions. It formers. Their kit line includes a number The assembly of the A-4 was performed is important to check and re-check wiring of basic amps, integrated amps, line stages by Ken Kawamura, a technician for VTV. to insure that your work is correct when and phono-preamps. For this article, we Ken's comments are as follows: compared to the schematic. The supplied chose to review their Model A-4 stereo schematic is correct, but a few of the amplifier kit. The A-4 is a 30 watt RMS 1. Helpful hints and proper solder proce- assembly instructions were incorrect. If per-channel basic stereo amp, featuring dures in the kit manual are beneficial for the assembly instructions conflict with the Ultralinear-connected push-pull EL34s the first time kit builders. Soldering codes schematic, refer to the schematic as the driven by two 12AU7s dual-triodes per (NS - not to be soldered yet) were helpful, correct way. ASUSA says the A-4 assem- side, in the classic Williamson circuit. AC but they left the soldering code out in bly manual has been rewritten and the voltage is rectified by silicon diodes. The some assembly steps, which left you won- step-by step instructions have been made power and output transformers are huge dering what to do. easier for the beginner. In addition, the and are custom manufactured to ASUSA resistor color codes have been added to the specifications. A filter choke is mounted 2. Chassis hardware, resistors, capacitors instructions for ease in identification. on the front of the chassis. (The choke in and wires came in separate bags. front of the chassis is now painted black, Sound Quality 3. A soldered parts placement pictorial fig- so it blends in with the overall cosmetics Once assembled, we hooked the A-4 of the amp.) ure in the assembly manual would be very helpful. Heathkit had these in their man- amp up to our speakers and a CD player. In the 1950s and 1960s, many quality uals, which aided in assembly and reduced Speakers used were either the Klipsch kits were produced by Heathkit, Knight wiring errors. Chorus Is or B&W DM110s. The A-4 Kit, Dynaco, Lafayette and others. The amp has relatively tight bass for an EL34 4. Insulated sleeving or shrink tubing was signs of a well-designed kit include a thor- amp, mids are full and highs are sweet and not supplied. The assembler will have to ough assembly manual, with an accurate extended, while not being overly bright. parts list, proper marking of parts, and purchase this at an electronics supply This amp has good color and overall tonal store. Screws to mount the rubber feet diagrams that go through the assembly balance. Acoustic instruments sounded were missing from the package. process, step-by step. The ASUSA Kit realistic without any bloating of the mid- came with a 15 page assembly manual that frequencies. It was very neutral sounding 5. A few areas of the assembly instructions and easy to listen to for extended periods included: tips on assembly and wiring, were confusing. There were a few labeling proper soldering procedure, amplifier spec- of time. The A-4 has enough power to be errors, such as specifying a 1 watt resistor used with modern acoustic suspension ifications, circuit description, step-by step where a two watt was required. Tech sup- assembly instructions, wiring instructions, speakers having a sensitivity rating of 89+ port had to be called a few times to clarify dB/1 watt/meter. Input sensitivity is high instructions. enough for you to plug a CD player or Fortunately, tuner (with volume control outputs) ASUSA tech straight into the amp without using a pre- support was amp. helpful and easy to talk with. Like all new equipment, break-in is required for things to smooth out. We ran 6. Some minor the amp for about 30 hours and noted an things were overall sonic improvement in the mids and noted after the highs which made the amp sound more amp was finally musical. Sonically, the A-4 is superior to assembled any similar-priced tube or solid-state according to the amplifier on the market. supplied instructions. Why would you want to go through the The power pilot trouble of upgrading a rusty old Dynaco light went on Stereo 70 you found on EBay, when the when the power ASUSA A-4 will sonically outperform the was shut off and ST70 and many other vintage EL34 power went off when amps? This is due in part to the all-triode

V AC U U M T UBE V ALLE Y ISSUE 11

22 A S U S A A - 4 A M P L I F I E R K I T front-end circuit of the A-4, as well as the be replaced with either 5-Way speaker have fun building this kit and will be able A-4 output transformers which are more binding posts or larger speaker terminal to tell their friends "I built it myself." balanced and neutral sounding than the plates with minor modifications. All of us at VTV agree that the A-4 is a Dynaco A-470s. With the A-4, you can start with a new chassis, new parts and If you can build this kit, you will also qualified BEST BUY tube amplifier kit. high-quality transformers instead of try- have developed the skills to conduct cir- The ASUSA A-4 has the most bang for ing to undo some 1960s kit-builder's flaky cuit component upgrades. Some buck of any tube amp kit currently on the market in the USA. In addition, this kit soldering joints on butter bricide circuit improvements can be achieved by chang- is ideal for customers in foreign countries boards. In addition, replacement parts ing the stock .1 uF coupling capacitors to for vintage amps, such as high voltage Hovland MusiCaps, UltraTone Capacitors due to the multi-tap power transformer. quad capacitors, are difficult, if not or other upgrade caps of your choice. 230, 117 and 100 volt AC taps are avail- able on the stock AC power transformer. impossible, to find. The premium capacitors will make the amp sound somewhat bigger and more Advertised Specifications Sonic Improvements and Upgrades extended. Additional improvements can be made by removing the silicon power Frequency Range - 25-25,000 Hz @ 1 dB Many audio enthusiasts consider the supply diodes and replacing them with Distortion - Less than 1% at 30 watts EL34 their favorite output tube because fast switching FRED diodes in the TO- of its detail, power and romantic sound. 220 case. Lastly, the B+ filtering could be Hum and Noise - Down 70dB In addition, the EL34 is in current pro- doubled from the two 20 uf @500 V to Sensitivity - Less than one volt input for 30 duction by several manufacturers and two 47 uf @ 500 V for a little more bass. watts output affordable. The A-4 comes equipped with Higher quality electrolytics could also be Line Input Impedance - 500K Ohm a quad of Svetlana EL34 output tubes. In used to add an even smoother sound. our VTV listening comparisons, the ASUSA tells us that there is no warranty Size (w/d/h) - 14" x 10" x 6.5" Svetlanas come very close to the sound of on the kit, but transformers and all other Net Weight - 34 lbs (15.5 Kg) the original Mullard EL34s from the components are warranted for 90 days. ASUSA-Kit, 6717 NE 181st Street, 1960s. N.O.S Mullard EL34s are now Seattle, WA 98155 USA $75-$150 each or more, and hard to find Product Rating (425) 481-8866 in matched quads. I suppose you could notice some improvements by spending At a base price of $549. the ASUSA A- ASUSA A-4 Measurements at the One another $300 or so on Mullard EL34s, 4 amplifier kit is an excellent value for the Electron Laboratory but significant sonic improvements can be money. A chrome-plated chassis and tube made by substituting higher quality NOS cage are optional at extra cost. If kit The ASUSA A-4 comfortably exceeded its 12AU7s. Good 12AU7 candidates builders take time to carefully assemble advertised specifications. The maximum include the Brimar ECC82, Mullard this unit, they will be very satisfied with output power before clipping was 36 watts ECC82, Siemens 5814, Telefunken the results. If you need at least 20-30 and THD was .55% at 30 watts. The high smooth plate ECC82, RCA 12AU7 watts to drive your speakers, most single- frequency response varied between channels: cleartop, Radio Technique (France) 6189 ended amps will not work well. The A-4 the right was -1dB at 47.6KHz, the left was or 5814 and CBS 7730. has ample power to drive most moderate -1dB at 58.6KHz. The low power, low fre- efficiency (89 dB+) bookshelf speakers quency response was essentially flat to As noted above, input sensitivity is with ease. This kit is perfect for the per- 20Hz, although showed a ldB rise at 10Hz high, so if your preamp has any hum, this son who is bored or irritated with solid- - a sign of potential low frequency instabili- amp may pick it up. The speaker termi- state amplification and wants to buy their ty. At 30 watts output, the lowest frequency nals are a little on the small size and will first tube amplifier. In addition to saving before saturation was 23Hz, which is quite not accept 8 gauge spades, but they can hundreds of dollars, the kit builder will good and a testimony to the quality of their large output transformers. The noise mea- surement was better than -74dB (referenced at 30 watts) and was not dominated by hum. Sensitivity was 0.56Vrms in for 30 watts out - a bit more sensitive than most amps, but still reasonable. A "passive pre- amp" would work well here.

The harmonic distribution was typical for a class-AB1 push-pull amp - higher odd har- monics. At 5 watts and above, there were fairly high amounts of high-order harmonics - at least up to 17th order. Crosstalk between channels was a bit marginal - rising to -46dB at 20KHz. At 150Hz it was at a minimum of -76dBm but rose to -55dB at 20Hz. Shunting the main power supply fil- ter electrolytic capacitors (C22 and C23) with 100uF 500V capacitors reduced the low-frequency cross-talk by over 10dB.

John Atwood, VTV Tech Editor

V A C U U M T U B E V A L L E Y IS S U E I 1

23 O T L H E A D P H O N E A M P P RO J E C T

resistors to get the correct voltages. For Kludge 4 Single-Ended example, you could use a 115V isolation transformer to supply the B+ for the out- put tube, and increase the value of the 18 OTL Headphone Amplifier Project ohm resistor proportionately. Capacitors are heavily derated in voltage in this design to allow you to do this. By Scott Dorsey © 1999 All Rights Reserved Let's take the output stage supply first. The 90VAC output of the transformer is For studio use, I found myself in need that it can be done is something impres- rectified and run through two 470 uF of a headphone amp that could drive sive in itself). 200V capacitors in parallel, then through high-Z studio like the AKG a smoothing resistor, and to a set of three The design can be built on a conven- K240, which require a substantial voltage more 470 uF 200V capacitors. These val- tional BUD chassis with point to point swing to get reasonable levels. On the ues were chosen because they are common wiring. Both tubes take standard octal other hand, I also found myself in need of items in PC power supplies and are there- sockets and are readily available from a headphone amplifier that could drive fore cheap commodity items (and can standard sources from Triode Electronics low-Z headphones like the Grado, prefer- even be scrapped from old computers by to Antique Electronic Supply. Readily ably with several headphones paralleled the adventurous), and they are about the available components were used in every together. minimal capacitance acceptable for good case, except that of the power supply hum rejection and good sound quality. transformer. Out of this need came the Kludge-4 Some tests were made with regulated sup- headphone amplifier. This is a simple plies which gave better noise rejection but two-tube headphone amplifier with a Power Supply somewhat grainier sound, so I decided to high-transconductance regulator tube The power supply is called upon to pro- go back to the simple brute force used in cathode follower mode for fairly vide 90V at substantial current (about approach. Notice those ceramic caps wide voltage swing and a very low output 300 mA) for the output tubes, 260V for there? They are bypass caps to stiffen impedance. It is, in fact, even possible to the input tubes, and 6.3V at three amps things up at RF a bit. By using them, you drive the 16 ohm Quad loudspeakers with for the filaments. The original design used can get away with using cheaper bridge this amplifier if one is willing to suffer a custom-built transformer, but you can rectifiers and not having any sonic degra- some reduction in low end. (I cannot rec- use individual transformers for the output dation from some of the switching noise, ommend actually doing so, but the fact stages, so long as you adjust the series though they aren't really essential.

2x 470µF 1800 3e 470gF AC 250V 5W 250V 90V Line

106 f pF

eadphone Output

Figure I Il Kludge 4 OTL Headphone Amplifier

1.0µF 320V 10K 260V AC Line 6080

AC Line

In Left 4.70 2K 2W In Right

8 6SL7GT

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"2 4 O T L H E A D P H O N E A M P P R O J E C T

The input supply is similar, just higher from 10K to 100K will work, so see what 1K resistor to ground keeps that offset at voltage and much lower current. A 600 quality pots you have on the bench. (Pots all times (as well as reduces popping by VCT transformer is half-wave regulated, below 50K may load down some tube pre- charging the cap up quickly even with no run into a 160 uF 360V to amps.-Tech Ed.) I can strongly recommend load on the amp). These, combined with ground, a 10K resistor, and then another the Noble and higher grade Alps pots the bypass caps, do as much as possible to 160 uF cap. These capacitors also are which are available for reasonable prices reduce the ill effects of the electrolytic, commodity items; the Nichicon and have excellent tracking between chan- and indeed with AJB tests between large nels. With headphones, film cap arrays and the bypassed elec- mistracking that would be trolytic, the sonic difference was found to inaudible on speakers can be small (although still audible). become painfully obvious due to the exaggerated Construction Hints imaging. The pot drives I have built several of these in small half of a 6SL7GT acting as Bud chassis, and one of them in the case a capacitively coupled of an old IBM PC power supply. The amplifier, with a gain of transformers and the output tube are the about 50. limiting factors here (and yes, before you ask, you CAN use a 6AS7 in there, Output Section though it will sound different) in terms of It's single-ended! Because size. the two channels share a Because even a slight amount of hum common ground, fancy low-Z stages like bridged can be a major problem with sensitive headphones, be very careful about your configurations or the Wiggins Circlotron are out grounding scheme. You will need to use single point grounding, and eliminate all of the question. It's possi- ground paths through the chassis. In a ble to do a totem-pole cir- perfect world, this would mean that the Kludge 4 Front View cuit with two drive devices, but I never found those to chassis was connected to the signal ground at only one point. In reality, balance well or sound good unless you use isolated ground connec- photoflash caps of these values are intend- (since after all, tubes don't come in PNP tors, it will be connected to the ground at ed for use in disposable cameras and can versions). So we're back to the old friend, each one of the input and output jacks, be obtained at very low cost from Kellner the simple cathode follower. Capacitors or from scrapped disposable and that is acceptable. Nevertheless, you cameras at your local photo lab. This is a very hot-running cathode fol- want to avoid adding any additional lower, using a ground paths. Don't just use the loops The filament common 6080 around the tube sockets as grounding supply is a bit regulator tube. points, but use isolated standoffs and tie odd here. The The output them together at a single grounding 6.3VAC output (which has a point. from a trans- maximum former is used power transfer Overall, this is a design that has been optimized for good sound at very low to directly feed impedance of cost, and is a good performer at driving a the filament of around 40 the 6080 tube, ohms, just per- very wide range of different headphones. It can drive to high levels but does not which in itself fect for driving pulls 2.5A, a Grados), is sacrifice power for sound quality. very substantial capacitively This headphone amplifier project is amount of cur- coupled to the for personal use only; no commercial rent. Some of it, headphone sales or production of this design is per- however, is rec- jack, and we mitted. tified, smoothed are using a 100 and used to uF aluminum Mr. Dorsey ([email protected]) owns and drive the fila- electrolytic operates Kludge Audio, 217 Thomas Nelson ment of the with a 10 uF Lane, Williamsburg, Virginia 23185, a small 6SL7. Why, you ask? Some of the avail- film bypass cap to remove most of the studio specializing in classical and acoustic able 6SL7s, like the CBS and Sovtek electrolytic nastiness. If you are sufficient- music. He has several engineering degrees tubes (but not the GE or Raytheon tubes) ly rich and have sufficient chassis space, from Georgia Tech, and has been nominated have substantial filament-to-cathode leak- using 110 uF of paralleled film caps for Grammies several times. This and a dollar age. This causes substantial hum induc- would be a very good idea here, and the tion if the filament is run on AC. total voltage across it is less than 10V so will get you a cup of coffee. He is old enough you can get away with smaller caps. to remember when compactrons were going to Input Section be the salvation of the electronics industry. He The input section is a simple RCA jack The slight DC offset across the capaci- does not own a cat. tors minimizes problems with the elec- going into a passive volume control. I trolytic nonlinearities near zero. Plus, the picked a 20K control here, but anything

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25 VTV L I S T E N S T O C A P A C I T O R S

ESR, they are a good sounding capacitor. good following. Their product line fea- VTV Listens to Earl Yarrow, Steve Parr, and other vintage tures a huge variety of values and types of Signal Capacitors hi-fi equipment restorers say that precision capacitors using foil and film ICM WRs sound very warm, but detailed metallized film, teflon, etc. We listened and musical. The IC-M WR sonics and to the polypropylene foil and film types By Charles Kittleson speed are very close to the original design- and noted them to be accurate, fast and ers intentions for classic equipment. IC- very detailed sounding, especially in high- © 1999 All Rights Reserved M WR caps are an excellent choice if you end audio designs. In fact, they are used are restoring any type of vintage tube gear by many OEMs of tube and solid-state or re-capping crossovers in vintage speak- audio equipment. Note: Rel-Cap also Although many capacitor manufacturers ers. markets the popular Multi-Cap capacitors. make claims on how great their capacitors If you plan on using Rel-Caps in vintage sound, few subjective listening evaluations 716P SBE Orange Drop audio gear, the foil and film types seem to have ever been published. At VTV, we be more desirable for maintaining the The venerable orange drop has been original vintage sound. have experimented with many different around since the 1950s. Orange Drops types of capacitors and have formed some are now made by SBE. For years, it was Hovland Musicap - Polypropylene Film listening impressions. There are several used as a quality replacement cap in and Foil high-quality capacitors on the market and radios, TVs and amplifiers. Many manu- Hovlands are attractively packaged, have the selection is growing continuously. Due facturers, including Fender, used them in silver plated stranded leads and are very to time constraints and other factors, there is production. There are several varieties of well-made. They are available in most no way we could possibly evaluate all brands Orange Drops, but the highest quality is standard values for bypass, coupling and of capacitors in this discourse. To speaker crossovers. Many amp help our readers understand repair customers specify Hovland some capacitor sonic differ- MusiCaps when restoring their ences, we listed a few capacitor tube amplifiers and preamps. types we've had good results Sonic improvements with with. These may be good choic- Hovlands include smoother es for you, depending on the response and improved bass per- application. formance. In addition, unlike For our listening evaluations many modern caps, they are easy we used two amplifiers, an to listen to and tend to have a Antique Sound Lab A-4 push- sweeter high frequency perfor- Capacitors (Top l to r): Rel-Cap, pull EL34 power amp and a mance than other some premium IC-M W!?, Silver Ultra-Tone, custom single-ended 300B amp caps. 716l) Orange Drop, Nichicon with One Electron UBT-3 3K output transformers. In addi- Ultra-Tone - Silver Foil in Oil tion, we used a vintage Dynaco Ultra-Tone Silver Foil in oil-capacitors the 716P polypropylene film and alu- Stereo 70 and a Fisher 500C receiver. For are made in England using 98% silver foil minum foil with solid copper leads. Sonic this test, we connected the capacitors into the wound with high-quality paper impreg- qualities of Orange Drops depend on the coupling circuit between the driver tube and nated with non-toxic, mineral oil as a application. In hi-fi coupling stages, they the output tubes. dielectric. Ultra-Tone Caps are less likely can have a tubby bass response and some- to have electrical or oil leakage when com- what smeared highs. However, the mid- Some tips: Remember to wire signal pared to other modern oil types. Ultra- frequencies can be big and musical. This capacitors so that the inner foil points Tone Caps are sealed with epoxy on both toward the output and the outer foil points can work well in guitar amplifiers and in certain hi-fi applications. ends and feature solid-silver plated OFC toward the input. The outer foil was axial leads. sometimes identified with a printed band Nichicon Metallized on older caps and normally is on the left Ultra-Tone Silver Foil caps seem to have side of the capacitor when reading the The Nichicon metallized polypropylene excellent musical realism." The sound pre- printed information on the cap. If you capacitors are an inexpensive alternative to sentation is rich, vibrant and liquid. wire the outer foil to the output side, the some of the other capacitors listed here. Other modern and vintage paper in oil sound will be muffled and rolled off. If in They feature radial leads, are compact and caps can sound darker or veiled by com- doubt, try reversing the leads. Also, avoid durable with a hard epoxy coating. Sound parison. Silver Foil Ultra-Tone-Caps are a using the same brand and type of capaci- quality is detailed, but a little on the good choice for single end triode ampli- tor throughout the amplifier. Mix and bright side. Some feel that a good appli- fiers, push-pull power amplifiers, tube match capacitor brands and types (oil, cation would be upgrading guitar amps preamps, power supplies and premium film, paper, etc.) like you would add spice and "darker" sounding amplifiers or pre- loudspeaker designs. or seasoning in your favorite dish. amps. They are not as "full bodied" as some of the other caps listed here, but are This short article is a subjective evalua- Illinois Capacitor MWR - Metallized worth experimenting with due to their tion of some capacitors types we like. It Polyester bargain pricing. by no means is exhaustive and we plan to feature more articles on capacitors in John Atwood, VTV Technical Editor, Rel-Cap Polypropylene Film and Foil future issues of VTV. has measured and tested IC-M WR capaci- tors and noted that even though they are Rd-Cap has been selling precision not super fast and have slightly higher audio capacitors for several years and has a

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26 V IN T A G E M IC R OP H O NES A N D S P E A K E R S

Vintage Note: The prices listed below (in Japanese ESL-63 Electrostat Y300,000 pr Yen) were derived from MJ Magazine. RCA Due to time and space constraints, the Microphones and LC-1A 15 inch coaxial Y580,000 pr list below is not all-inclusive. Speakers in Japan Tannoy Speakers 12 inch gold f480,000 pr By Charles Kittleson AR 15 inch gold Y550,000 pr © 1999 Ali Rights Reserved AR-1 Y200,000 pr 15 inch red Y850,000 pr Altec 15 inch silver Y900,000 pr High quality speakers have been a hot Y1,250,000 pr Autograph Y1,780,000 pr commodity in Japan for over 30 years, A-4 especially certain brands. Like anything A-5 Y780,000 pr Westminster Y650,000 pr vintage or classic, there is a certain mys- A-7 Y430,000 pr York Y850,000 pr Model 19 Y480,000 pr 288(B, C) x200,000 pr 311-90 Y180,000 pr 515B Y150,000 pr 803B Y240,000 pr 604A Y430,000 pr 604 8K 1360,000 pr 755A Y200,000 pr 802B Y75,000 803B Y130,000 pr WE Studio Ribbon Mike tique surrounding brands like Tannoy and 806 (8A) i70,000 pr Western Electric. There are literally fl 60,000 pr University dozens of shops in Tokyo and other Asian 1005 6201 Y m000 pr cities that specialize in the sales of vintage Electro-Voice Western Electric audio equipment. For the most part, clas- Patrician 800 Y2,200,000 pr sic audio equipment in the US is not con- TA 4151A 12 inch woofer k750,000 pr SP-12 v70,000 pr sidered a status symbol as it is in Japan. TA-4181A 18 inch woofer k600,000 pr SP-15B Y120,000 pr Western Electric speaker components WE 21A horn Y600,000 pr 12TRXB Y70,000 pr designed for movie theater applications WE 22A horn Y480,000 pr are especially valuable. These were never 15TRXB Y160,000 pr WE 555 horn driver k490,000 pr sold to the public, but were leased to the- T350 Y90,000 pr WE 594A horn driver Y900,000 pr aters for a certain time period. When the JBL lease was up, speakers and equipment WE 597 horn w/driver Y1,200,000 pr Y3,000,000+pr were occasionally sold to theater owners Hartsfield WE 728B 12 inch speaker Y650,000pr and operators. Paragon Y1,500,000 ea WE 755A 8 inch speaker Y480,000 pr C31 Y1,600,000 pr Speakers in large cabinets, such as EV Y580,000 pr Microphones Patricians, jBL Hartsfields, Jensen C34 Altec Imperials, etc. usually turn up at auctions, C36 k380,000 pr 639B Y1,500,000 estate sales, via older hi-fi enthusiasts and D-130 Y80,000 pr word of mouth. Fast-buck dumpster EV Y110,000 pr divers typically scrapped lesser model D-130A 556 Elvis mike Y850,000/pr wood cabinets to get at the raw drivers 075 y70,000 pr RCA and crossovers because they are much easi- 175-DLH Y110,000 pr er and cheaper to ship to Asia. 44DX Y2,500,000 375 (grey) Y290,000 pr Consequently, many cabinets wound up as 77DX Y2,300,000 firewood or mulch. Quality speakers in 4344 Y1,240,000 pr Neumann original cabinets command super-high LE-85 Y80,000 pr M49 Y17,000,000 prices in Japan because they are very Jensen expensive and troublesome to ship. U47 Y9,500,000 A-12 f120,000 pr U67 Y5,800,000 For top prices, the speaker cone must be G-600 Y550,000 pr original with no holes or repairs. Non-fac- Western Electric G-610 Y980,000 pr tory reconed speakers are not knowingly 7A Y9,000,000 purchased by collectors and in some cases H-222 Y150,000 pr 9A Y10,000,000 are even difficult to sell to end users. M20 Y650,000 pr Speakers are also very difficult to ship. 639 Y1,600,000 QUAD Typically, they must be mounted on a 640 ¥7,500,000 wooden baffle board and double-boxed. ESL-57 Electrostat Y180,000 pr

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27 T ES T B E N C H : P O W E R S U P P L I E S

The Audio Test Bench their electrolytic capacitors. (see VTV, Power issue 3, page 26). Basically, the equipment is plugged into the variac, turned on, and the AC voltage slowly raised over a period nfire o of minutes to an hour or more. The grad- 0. 0 by Supplies 0 0 0 0 0 o ual rise in DC voltage across the filter • 0 0 • O 0 C ) John Atwood © 1999 All Rights Reserved capacitors re-forms them and can bring 1 =1 them back to life. There are two problems with this method, though. One is that is essentially impossible to check which capacitors are drawing too much current and need slower forming. You just So far our Audio Test Bench series has the load, as shown in figure 1. When concentrated what is considered tradition- cold, a tungsten filament has low resis- al test equipment: meters, scopes, analyz- tance, but as it heats up, the resistance ers, etc. In this issue, we will cover one increases, thus serving to limit the current part of the infrastructure of any test flow to the load. The brightness of the bench: power supplies. These can range bulb also is a visual indicator of the rela- from the simplicity of a current-limiting tive current flow. It is hard to get accurate light-bulb all the way to computer con- current control with light bulbs, though, trolled regulated supplies. Somewhere in and nearly impossible to bring up a load between will be the ones best suited for slowly from zero volts to full voltage. your test bench. A solution to the slow bring-up prob- A power supply is defined here as a sys- lem is the adjustable transformer, com- l'hu:.1 1: Cna-it.44 Variac tem of delivering power — AC or DC — monly known as the Variac. The word with at least one controlled parameter, Variac was the trademark of the General typically voltage or current. Many modu- Radio Co., who invented it in the early increase the voltage and hope that noth- lar power supplies exist for use inside 1920s. However, with the decline of ing blows up! On the other hand, equip- equipment and some of them are usable General Radio (later named GenRad and ment that has been used recently often as test equipment, but most of the sup- eventually QuadTech) and the very com- needs no forming at all. The other prob- plies considered here are self-contained mon use of the word, variac has essential- lem concerns equipment with vacuum units intended for bench-top use. ly passed into common usage. A variac is tube rectifiers. A tube rectifier will not start conducting until its heater voltage is

CAUTION: Many of the supplies Fuse has same at least 1/3 to 1/2 its rated voltage. If a rating as variac Figure 2 described here can have exposed high variac is used, no forming takes place voltage terminals! Exercise care to avoid Power Line until the line voltage is at least 50 volts lethal shocks! (for 120 volt systems). Then all of a sud- To Unit Under Test den voltage is applied to the capacitors in AC Line Power Supplies a rush, often damaging the rectifier and A means of adjusting or controlling the maybe even the capacitors. Tubes running AC line power to a unit under test is very - Safety ground — connect to chassis at below-normal heater voltage are espe- handy for initial bring-up (the "smoke cially prone to cathode stripping in this test") or for diagnosing power problems. situation. The solution is to either plug-in In most cases, a power generator is not a toroidal transformer with a carbon a solid-state replacement rectifier or form needed, just a scheme for controlling the brush that rotates as the control knob is the capacitors with a DC supply as voltage and/or current to the load. One turned, giving a smoothly varying AC explained later. exception, rarely encountered on the voltage from 0 to typically 120% of the audio test bench, is the need to generate a incoming line voltage. A variac does not Unregulated DC Supplies different power line frequency, such as inherently regulate the AC voltage or cur- Direct-current (DC) power is needed 50Hz in North America, 60Hz in most rent, but when used with a voltmeter and for a variety of test bench functions: pow- other places, or 400Hz to run surplus ammeter, allows easy manual adjustment. ering solid-state circuits and digital logic, military avionics. Raw (unpackaged) variacs are easy to find tube heater supplies, and tube plate (B+) in surplus — just check the rated voltage supplies. Regulated supplies, described in To Unit and current and make sure it is not a Under Test the next section, are usually the preferred, 400Hz unit! Figure 2 shows a good way and sometimes the required type of sup- to make a bench-top AC supply using a ply, but in some cases can be prohibitively variac. The fuse is necessary, since the expensive. An unregulated supply with a variac does not limit the current and will voltmeter to monitor its output can be Load current x Line voltage Total lamp wattage 2 be damaged if the load short-circuits. very handy for temporary test set-ups that Photo 1 shows a nice bench-top Variac by need a lot of voltage or current. Figure I General Radio with voltage, current, and power metering. A commercial adjustable high-voltage One of the simplest and oldest methods supply is shown in Photo 2. It is basically of limiting AC power to equipment is to One of the main uses of a variac for a conventional capacitor-input supply use one or more light bulbs in series with tube enthusiasts has been the slow bring- using two 5R4GY rectifiers, with the up of old equipment in order to "re-form"

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they can be adjusted upwards to purist will find the occasional need for a 6.3 volts. If, however, the output DC filament or bias supply. Anyone voltage abruptly drops as you working with op-amps will need a dual adjust it above 5 volts, the supply supply capable of + and — 15 volts or has a "crowbar" circuit originally more with at least 200 mA current capa- intended to protect logic from a bility. Good quality low-voltage bench- power supply failure. This is typi- top supplies are hard to find cheap in sur- cally an SCR (Silicon-Controlled- plus, due to their universal usefulness. Rectifier) across the output — Expect to pay at least $50 or more. A new which can be removed. supply will run from $75 to over $300.

One concern about computer High voltage supplies (over 150 volts) power supplies is whether to use a are a different story. Many thousands linear or switching supply. A lin- were made during the vacuum tube era, Photo 2: Unregulated Tube-Type Power Supply ear supply is the same as used in and technicians who need high voltage nearly all audio systems: a large today generally don't want a 40 year old high-voltage transformer driven by a vari- laminated-iron power transformer fol- tube-type boat anchor. That leaves lots for ac. A filament transformer wired ahead of lowed by rectifiers, capacitors, and a regu- us tube-o-philes! These old vacuum tube the variac supplies the 5 volts for the rec- lating pass transistor. These are not very regulated supplies generally put out 400 tifiers as well as 6.3 volts to the front efficient and are heavy, but are inherently to 500 volts at from 100 to 500 mA, panel. quiet. A switching regulator rectifies the although I have picked up an old If you are experimenting with transmit- power line directly, then uses sophisticat- Dressen-Barnes supply that was rated at ting tubes, a heavy-duty low-voltage DC ed switching circuitry to convert the DC 0-1000 volts at 500mA! These supplies supply is needed for their filaments. into high-frequency AC, which is then nearly always have an unregulated Typical voltages range from 5 to 20 volts run through a small ferrite transformer 6.3VAC output for running tube fila- at up to 10 amperes. You can build such a and rectified again. Their main advan- ments and some have a very low current supply from a surplus low-voltage, high- tages are very good efficiency and light (< 5mA) negative 0-100V output that was current transformer followed by a rectifier weight. They are complex and used to be intended as a tube bias supply. and filter capacitor. If you have a bench- expensive, however. If not filtered and well-shielded, switching supplies can The common brands seen for tube top variac, you can use this to adjust the power supplies are: Lambda, Kepco, output voltage. spread their switching transients into sen- sitive circuits. Most modern supplies Dressen-Barnes, Oregon Electric, Heathkit, EICO, Fluke, Hewlett-Packard, Regulated DC Supplies switch at over 20KHz, though, and I've heard several very good home-built as well as many minor brands. Bringing If you can afford it, regulated power sounding amplifiers that have used up and restoring an old power supply is supplies are the best choice. They have switching supplies for the heaters. One similar to restoring an old power amp: low ripple (low hum), can maintain a other point about switching supplies: check the tubes, re-form or replace the steady output under load, and maintain most have very effective current-limiting electrolytics, replace tubular paper capaci- that output accurately over time. Their to protect against destructive shorts. Since tors, replace any selenium rectifiers with main drawbacks are cost, complexity, and tube filaments can briefly draw up to four silicon, and check for burned resistors or sometimes lack of ruggedness. times their normal current when cold, other damage. Aside from burned-out switching supplies can shut down when transformers it's not hard to get these sup- The explosion of computer technology plies working. has resulted in massive quantities of fixed- trying to drive filaments. The only real voltage modular supplies on the surplus solution is to use a supply that has at least Be careful! — Deadly voltages and market. These can be very useful for fila- 3 to 5 times the current rating of the currents are present in this equipment! ment supplies. The most common voltage tubes. Discharge all filter capacitors before available is 5 volts, needed for TTL-com- Bench-top low-voltage adjustable regu- working on the circuit and never solder patible logic. These can be used as-is to lated DC supplies are a necessity for any or make changes with the power cord run 300B filaments, for example. Many solid-state work and even the all-tube plugged-in! of them have enough "head-room" so that

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Photo 4 shows an incredibly heavy "Unlike the dielectric in other there will be a steady current draw that Lambda Model 50 bench-top supply. capacitor types, the film is subject to linearly increases with voltage which can Lambda also made a line of narrow rack- deterioration in spots where foil confuse the re-forming process. If this is a mount supplies that are also amazingly impurities are present, when the problem, you may want to temporarily heavy. Photo 3 shows a PS-3 Heathkit capacitor is stored for long periods. disconnect one end of the capacitor from regulated power supply, very common and When full voltage is again applied, the circuit while forming it. Gas tube reg- usually easy to find at swap-meets, etc. leakage currents at these spots may ulators will cause a sudden jump in cur- be large enough to destroy the weak- rent — these can be removed if needed. Specialty Supplies ened film before it can be repaired Occasionally you come across a capaci- Occasionally you will come across some by electrolytic action. Consequently, it is inadvisable initially to apply tor that either doesn't capacitate — no odd-ball tube-type power supplies. These charging current whatsoever, or one that can be useful, depending on your inter- full-rated voltage to a capacitor which has been at zero voltage for never seems to form. Also, you may see ests. You may see a "Constant-Current" many months. Also, since heat accel- signs of previous leakage: cracks in the supply. These appears similar to conven- rubber seal or dried up white crusty mate- tional tube-type but will have a "maxi- erates deterioration of the film, this precaution becomes particularly rial. In all these cases, replacement is nec- mum voltage" or "limiting voltage" con- essary. However, in most cases, if carefully trol. These supplies have a high-imped- important when the capacitor has been stored in the tropics or other done, even very old capacitors can be ance output that supply constant current. hot places. Electrolytic capacitors brought back to life. The limiting voltage control is analogous give most satisfactory service under to a current-limiting control — it limits the maximum output voltage in this case. continuous operating conditions." These are not especially useful for power- This was written in 1946, and even by References: ing regular circuits, but are ideal for pow- the 1950s electrolytics had improved 1. Capacitors — Their Use in Electronic ering an incremental inductance bridge, enough that the time before reforming is Circuits, M. Brotherton, D. Van something any transformer or choke per- necessary is usually years, not months. Nostrand Co., 1946. (A very practical son will be interested in. The easiest method of re-forming filter book on capacitors by a member of the capacitors is to connect the positive lead Bell Labs technical staff. Doesn't cover Sometimes you will see high voltage of an adjustable supply to the rectifier new types like plastic film or Hi-K ceram- supplies that go up to 2,000, 5,000, or output (or the first capacitor in the filter- ic types, though.) even 30,000 volts! If these can fit on your ing chain) and the negative lead to test bench then they are too low in cur- ground. This allows all the capacitors in 2. Electrolytic Capacitors, P. McKnight rent for a transmitting tube amp project. the filtering network to re-form together. Deely, Cornell Dubilier Corp., 1938. (A Anyone experimenting with electrostatic With an eye on the current meter, slowly bit dated, but exhaustive treatment on speakers may find these handy, though. bring the voltage up from zero. You will electrolytic manufacturing and use.) The high-voltage safety warning is espe- see the current jump up and then fall back cially important with these supplies. Use 3. Electronics — Experimental down — this is normal and is just the extreme care! Techniques, McGraw-Hill Book Co., capacitor charging current. What you are 1949, WC. Elmore, M. Sands, (Book 1 of looking for is the steady current. If it is Division V (Los Alamos) of the National Capacitor Forming higher than 5 to 10 mA, then back off the Nuclear Energy Series. Chapter 7 has Aside from powering prototype circuits, voltage. You will then see the current good regulated supply theory plus many an adjustable high-voltage supply is slowly decline — this is the forming taking circuits well-explained.) invaluable for re-forming old electrolytic place. Once the current has declined to capacitors. As mentioned earlier, using a less than 5 mA, crank up the voltage a bit 4. Electronic Instruments, variac is not the best way to re-form the more, and continue this process until you IA. Greenwood, J.V. Holdam, D. Macrae, capacitors. Some capacitor checkers, such have reached the lowest rated voltage in McGraw-Hill Book Co., 1948. (Book 21 as the Sprague Tel-Ohmike, provide a cur- the filter chain. On severely unformed in the famous MIT Rad-Lab series; chap- rent-limited voltage for re-forming. capacitors, this process can take several ters 15 and 16 have an excellent descrip- However, a DC bench supply also works hours, but more commonly it can be done tion of reference elements and tube regu- very well and can provide feedback to you in 5 to 10 minutes. If the capacitors had lator design.) on how the forming process is going. already been formed, you may not see any First, a little capacitor theory. residual current at all. If you don't want to 5. DC Power Supply Handbook babysit the forming process, you can put a (Application Note 90), Hewlett-Packard, An electrolytic capacitor is made up of current-limiting resistor in series with the Harrison Division, 1967. (A good treat- two layers of aluminum foil separated by power supply, say 47K. You then wait for ment of solid-state linear power supplies.) paper saturated by an electrolytic paste or the voltage across the resistor to equalize. jelly. When initially manufactured, there 6. Kepco Power Supply Handbook, P. is no insulation present. Part of the manu- Things to look out for in the forming Birman, Kepco, Inc., 1965. (Kepco's view facturing process is to slowly apply a DC process include isolated capacitors and on solid-state and hybrid supplies. Good voltage across the capacitor. The resulting shunt resistors. An example of an isolated practical information.) current causes a microscopic layer of alu- capacitor is an electrolytic at the output of minum oxide to form, similar to the way a tube regulator. With the unit powered- aluminum is anodized. The thinness of off, the voltage from the main power sup- Next Audio Test Bench: Impedance bridges this layer is what give electrolytics their ply won't reach this capacitor. You will and component measurement. high capacity density. The problem with have to form it separately. If there are electrolytics is best explained by resistors from the B+ to ground, such as Brotherton in his small but excellent bleeder resistors or screen bias networks, book, Capacitors (p. 62; see reference 1):

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30 F A S T R E C O V E R Y E PI T A X I A L D IO D E S

Because they are usually fed directly because tube rectifiers still have a sonic Fast Recovery into a large reservoir filter capacitor in the edge. Solid-state diodes also raise the B+ power supply, rectifiers have to supply voltage. In addition, the mod may nega- Epitaxial Diodes large current peaks once every AC line tively impact the collectability of your voltage cycle. These peaks occur 100 or gear. Good vintage hi-fi candidates for 120 times per second and can be VERY upgrading to FREDs include: Fisher 400, By Charles Kittleson large, and very "spiky". If heavy filtering 500, 800 receivers, Fisher tube integrated and Eric Barbour and shielding are not used in the equip- amps with silicon rectifiers, EICO HF87 © 1999 All Rights Reserved ment design (and they rarely are), consid- and HF89, Harman-Kardon Citation II erable RFI (with a rich harmonic content) and V, H. H. Scott 340B receivers, from both these sources can be coupled Sherwood integrated amps and receivers, into the audio signal path, and even back McIntosh amplifiers, preamps and tuners, Most power supplies in tube audio Marantz amplifiers and preamps, etc. equipment use conventional diffused- into the AC line, to be coupled into other electronics. Even if you put a resistor Heck, they will even make most of your junction P-N type silicon diodes. Silicon solid-state gear sound much better! diodes are cheap and compact, but can directly between the rectifier output and the first filter capacitor, to help decrease sound awful due to their slow switching FREDs normally come in 600 and those current peaks, peaking and noise time and resultant tendency to generate will still be present. And, the DC regula- 1200 volt ratings and current ratings of noisy current spikes. one to 30 amps. Typically, diode peak- tion of the supply will be impacted nega- inverse-voltage ratings should be at least tively. OEMs started using silicon diodes in twice the DC supply voltage, because the the late 1950s and early 1960s, when the A quieter alternative is the Schottky rectifiers have to handle both positive and prices of decent high-voltage units became Barrier Diode. Unfortunately, Schottky negative AC voltage peaks. Example: if competitive with rectifier tubes. Silicon diodes suffer from a few disadvantages, the circuit will produce an operating volt- rectifiers were most often used in such as high reverse leakage currents com- age of 250 volts DC, it would require a receivers, integrated amps, preamps and pared to regular diodes. Schottkys are also FRED with a minimum of 500 volts rat- some power amps. Fisher, EICO, very limited in the peak-inverse voltages ing. Be conservative, as there is the added Heathkit, McIntosh and Marantz were they can handle. Nevertheless, for low- possibility of occasional line-voltage some of the first companies to utilize voltage supply rectifier applications, spikes. solid-state rectifiers. This way, they would Schotticys are outstanding performers, dispense with the rectifier tube, which You can use FREDs in bias, B+ and fil- widely used in the output sections of required another filament winding on the ament supplies. However, a more eco- computer-type switching supplies. They power transformer. And even today, many can also be used with success in filament nomical approach in filament supplies tube guitar amps and high-end tube com- would be to use Schottky diodes instead. and low-voltage bias supplies in tube ponents still depend on low-cost silicon equipment. Schottk-ys are inexpensive compared to rectifiers of the 1N400X family. FREDs and give excellent performance as What if the application requires higher power-supply rectifiers, if low voltages are Silicon diodes can sound bad because voltages? Fast Recovery Epitaxial Diodes involved. Schottkys are usually limited to they generate switching noise from their (FREDs) were developed initially by 60V PIV ratings. slow switching time in comparison to International Rectifier, in the early 1980s. tube rectifiers. There are actually two Even though they are far more expen- Tube electronics were not the intended sources of noise: the reverse-recovery application, as high-frequency switching sive than ten-cent 1N4007 diodes, time and the turn-on spike. (see next arti- installing FREDs in your power supply power supplies were just starting to cle) This slow recovery time has always can improve the sound of your system to become popular, forcing component man- been an issue with regular silicon (or ger- a greater degree than exotic cables or ufacturers to develop faster and more effi- manium, for that matter) rectifiers. other tweaks. cient devices. IR's trade name was HEXFRED. Now, several manu- facturers make FREDs, including IR, Harris, IXYS, General The Problems with Semiconductor, etc. Silicon Rectifiers

How Do They Sound? By John Atwood, When substituted into an Technical Editor © 1999 amplifier, compared to silicon diodes, FREDs have a full and airy sound. The bass is tightened When a conventional p-n junction rec- up, and the harsh edge in the mids tifier is forward-biased (conducting cur- and highs almost disappears. rent), many minority carriers (holes) are Details in the music start to come present in the n-silicon, just outside the out with greater clarity than ever junction. When the voltage across the before. FREDs sound as close to a junction is reversed, these holes must be tube rectifier as one can get, while swept out of the junction area before the not requiring additional power to rectifier will stop conducting. The result run a filament or heater. is an abrupt surge in current caused by the stored charge which then tapers down 1N4007, 1N5818 Schottky Diode, Don't go out and replace your as the holes diffuse out of the junction LYYS 11 and 8 amp FREDs tube rectifiers with FREDs,

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31 F AS T R E C O V E R Y E P IT A X IA L D I O D E S

crystal. This parasitic capacitance and inductance — Snubber networks and ultimately by electron transit times. absorb reverse reduces the decay time and turn-off current If silicon rectifiers have to be used, spike reduces the energy in the adding snubber networks across the recti- reverse current fiers will absorb nearly all the reverse cur- pulse. This rent surge. A simple capacitor across the technique is rectifier will smooth out the current called gold- surge, but not as effectively as the R-C Series resistor doping" and is combination. (See figure 1) limits capacitor used in "fast- The reverse current spike is not to be charging current recovery" recti- confused with the forward-current spike spike fiers. ("turn-on" spike) in capacitor-input recti- Figure I: Snubber Circuit The second fier circuits. This spike is simply the result technique is to of trying to charge a large capacitor area. This current spike contains a large use a rectifica- quickly and happens regardless of the rec- amount of high-frequency energy. This tion process that does not use any minori- tifier type. It is solely dependent on the can shock-excite any parasitic tuned cir- ty carriers that linger in the junction. The size of the capacitor and any series resis- cuits in the transformer or wiring. All this metal-semiconductor junction in a tance in the circuit. Adding extra series high-frequency energy can get into sensi- Schottky has no minority carriers, thus is resistance helps reduce this type of cur- tive circuitry. This problem is most acute inherently fast and low in noise. The rent spike. when the rectifier is drawing current HEXFRED and similar rectifiers use a when the voltage across it reverses, so is structure based on a power MOSFET — References: especially troublesome in choke-input cir- again a system that uses no minority car- 1. Application of Fast Recovery cuits. riers. Rectifiers, General Electric Application Note 200.38, J.H. Galloway, June, 1965. There are three main ways of reducing The third technique is to use a technol- the rectifier switching transient. One is to ogy where minority carriers don't even 2, Transistor Engineering, A.B. Phillips, reduce the hole life-time by adding exist: vacuum tubes! Tubes are inherently McGraw-Hill, 1962, pp. 145-148 "recombination centers" in the silicon fast — their speed is limited mainly by

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V AC U U M T UB E V ALL E Y ISSU E I I

32 V A C U U M T U B E V A L L E Y VTV Pro-Tube Shop Your headquarters for high quality audio parts 8. tubes P.O. Box 691, Belmont, CA 94002 USA (Order 10am to 6pm Tue-Sat) (650) 631-6550-Phone (650) 654-2065 FAX w w w.vacuumtube.com

Illinois Capacitors Illinois Axial Electrolytic Can Electrolytic ICM WR Metallized Polyester Capacitors Great Value and Capacitors 20,20,20,20 @475V (630Vdc rating) very dependable. 0.001 uf $0.80 ea 3.3uf @350V $1.20 ea (Mallory type) $29.00 0.002uf $0.80 ea 4.7uf @350V $1.45 ea 50+50uf @500VLCR 0.0047uf $0.80 ea 10uf @450V $1.60 ea w/clamp $21.50 0.0068uf $0.80 ea 22uf @250V $1.95 ea 100,100uf @500V 0.01uf $0.90 ea 22uf @450V $2.25 ea LCR w/clamp $28.00 0.022uf $0.90 ea 22uf @500V $2.85 ea 40,20,20,20uf @500V, 0.047uf $1.00 ea 47uf @35V $1.50 ea LCR w/clamp 0.068uf $1.20 ea 47uf @350V $2.50 ea $32.00 0.1uf $1.30 ea 47uf @450V $3.45 ea D.H.Labs Silver 0.22uf $1.60 ea 100uf @I 60V $2.95 ea Order: By email, FAX, Mail, Phone Sonic Wire 0.47uf $2.20 ea 100uf @350V $3.90 ea Minimum Shipping and Rated as the best 1.0 uf (400V) $2.50 ea 100uf @450V $4.90 ea Handling per order: sounding wire for the 2.2uf (250V) $2.75 ea 1000uf @25V $1.75 ea US $5.00, Canada $10, Europe $20, money by several 3.3uf (250V) $3.20 ea 2200uf ©35V $2.75 ea audio publications. Asia $25 (Heavier items will require 4.7 uf (250V) $3.80 ea "This is nothing other additional postage) 6.8uf (250V) $4.20 ea Hovland MusiCaps than a superb cable. It Polypropylene Foil and can be used with confi- $35 Minimum Order Ultra-Tone Silver Foil in dence with the finest of Paper and Oil Capacitors Film systems. Vintage Hi -Fi Rebuild Kits 98% pure silver foil in kraft paper High resolution, great-sounding film Make your own Get Great Sound & Save Bucks! impregnated with non-toxic mineral caps perfect for all types of audio speaker cable & All kits include all new ICMWR signal oil and petroleum jelly, sealed in equipment upgrades. interconnects. epoxy. Silver plated OFC leads with and bypass film caps, under-chassis elec- 0.01uf @1600V $9.79 ea Save BIG!!! inner foil marked (650Vdc rating) trolytics, 1 watt metal oxide low-noise 0.022uf@l000V $9.82 ea Silver Sonic T-14 plate resistors, new silicon power supply 0.01uf $12.00 ea 0.033uf @600V $8.01 ea Speaker Wire $4.00/ft diodes and schematic. Kits do not 0.02uf $14.00 ea 0.047uf @I KV $12.05 ea Silver Sonic BL-1 High include FP can-type electrolytics. 0.05uf $16.00 ea 0.1uf @600V $11.52 ea Definition Interconnect Wire $3.50/ft Dynaco PAS2/3 $45 0.1uf $19.00 ea 0.22uf @600V $14.55 ea Silver Sonic OFH-20 Dynaco Mark III $40 (for pair) 0.22uf $28.00 ea 0.47uf @400V $12.80 ea High Performance Dynaco Mark IV $40 (for pair) 0.47uf $40.00 ea 0.47uf @600V $21.71 ea Silver/Teflon Chassis Wire Dynaco SCA-35 $25 $70.00 ea 1.0uf 1.00uf @400V $21.66 ea $0.95/ft Dynaco ST-35 $25 2.0uf $130.00 ea 2.2uf @200V $23.83 ea RCA-2 Gold Tiffany- Dynaco ST-70 $25 Ultra-Tone Silver capacitors are 3.0uf @200V $28.45 ea Style Interconnect Plug EICO HF81 $55 superb performers. Our customers $1 0.95ea Note: Only the above EICO HF85 $45 think they are the smoothest, best- B-1 C Gold Banana Plug Hovland values in stock. EICO HF86 $35 sounding and most musical and Insulator $5.50/pr EICO HF87, HF89 $50 capacitors available. BSP Gold Mini Spade Tube Sockets Fisher X-101, X-202, etc $55 Speaker Terminals for $3.50 Ultra-Tone Polypropylene Octal Ceramic Chassis Vintage Hi-Fi $1.10 ea Fisher 400 Receiver $60 $3.00 Film & Foil Power Supply Octal Ceramic PC mt Fisher 500C Receiver $60 $3.50 Capacitors (Not Silver Foil) Octal NOS Phenolic A MEX, VISA, MC OK Fisher 800B, 800C $60 9 Pin Ceramic PC $2.50 20uf @ 650V $20.00 ea McIntosh MC30, MC40, MC75 $45 ea 9 Pin Ceramic Chassis $3.00 Send $3.00/US, $4.00/ 50uf @650V $40.00 ea McIntosh MC60 $50 ea 9 Pin Ceramic GOLD $5.00 US$ Foreign for our 24 $4.00 McIntosh MC225, 240 $65 100 uf @650V $60.00 ea 9 Pin Plastic w/shield page informative cata- 9 Pin NOS Brn Phenolic $3.00 McIntosh MC275 $75 FREDS (Fast Recovery Diodes) log with cool NOS tubes Scott 130 $80 parts and Vintage Hi-Fi. IXYS 600V 8A $3.50 ea Order Fast from our Scott 222, 222B, 222C, D $55 VTV Pro-Tube Shop, P.O. IXYS 1200V 11A $6.50 ea Scott 299, 299B, 299C, D $55 on-line catalog Box 691, Belmont, CA 60V 5 Amp Schottky $1.50 ea Scott 340B Receiver $65 vvww.vacuumtube.com 94002 USA

V ACU U M T UBE V ALLEY ISSUE 11

33 V A C U U M T U B E V A L L E Y

G) one electron Single-Ended Output Transformers ELECTRA-PRINT High Quality for a Reasonable Price Designed and Built in the USA AUDIO

QUALITY HANDWOUND S.E. OUTPUT TRANSFORMERS • Primaries from 1.8K to 10K • Exclusive wideband design • 16, 8, 4, or 2 ohm secondary • Gold plating CUSTOM-BUILT POWER TRANSFORMERS/CHOKES • Wound to your requirements UBT-1 Designed for parallel operation of: • Heavy-duty design for Class A use 1.6k primary 2A3s. EL34s, 300Es 6AS7s, • DC filament supply windings 15 watts etc. or Sweep-tube in • HV chokes to 15H, 300ma 160 rnA "enhanced triode" mode • Low voltage, high current filament chokes UBT-2 Component pricing and specifications catalog available 48k prim. . ' — Can be used with: 15 watts "119.uu 30013 50 SV811-3, etc. ELECTRA-PRINT AUDIO 110mA 1 4117 Roxanne Drive Las Vegas, NV 89108 ÜBT-3 3k Primani `c, Good for singler ended 702-396-4909 FAX 702-396-4910 110 wa"smA 1.19 .00 - 2A3 o 30013 Quantity discounts available

ANTIQUE ELECTRONIC SUPPLY LI I MP 6221 S. Maple Ave.•Tempe, AZ•85283 Phone (480) 820.5411 • FAX (480) 820.4643 or 800 706.6789 AFFORDABLE HAND-WIRED GUITAR AMP KITS!

HYPER DAC 24 / 96 with HDCD Available with Jensen Stereo Digital to Analog Converter speakers! Three digital inputs, AES/EBU, SÍPDIF and TosLink With vacuum tube output circuitry. $2100.00 a 0..

Based on blackface era amps from the mid 60s, these Pr all-tube guitar amps feature 3-knob reverb control, tube rectifier, solid-pine jointed cabinets, bias setting jacks, master volume control, heavy aluminum chassis, cloth cov- ered wiring, full size potentiometers, vintage style tube sockets, 40W 2x6L6 output, carbon composition resis- tors, Mallory tone capacitors and many other top features. 2x12 TONESavor $799 2x10 Old Flame $749 (De ta QC)

Phone: (606) 485-6423 ; ; Fax: (606) 485-6424 LEN 1746 Ivar Ave. Hollywood CA 90028 E-Mail: [email protected] www.iguitar.com/allen 323 H011ywood 7-4300 AMPLIFICATION fax 323 464-9100 Quality tube amps, VIS4 Masi&Card web www.mothaudio.corn kits and parts maim

V A C U U M T U B E V A L L E Y ISS U E I I

3 4 V A C U U M T U B E V A L L E Y

Vacuum Tube Testing and Matching System

• Instantly identify weak or , blown tubes • Quickly measure tubes for amplifying capability • Precision-match tubes for plate current and/or transconducta • Save money on third-party matching costs - • Increase sales of matched sets by verifying custorners tubes • Incoming QA Check for OEMs or music stores • Create your oWn label tube sets

The Maxi-Matcher Digital Tube Tester measures any of the stan- dard ocia'171?aSe.PONVer pentodes for Plate Current (Ip) and Trausi:Ondrictance .(GM) chafdctcristics, and with optional adaptors Maxi-Test'Company will also test nine-pin pentodes. NOvar pér ,:nr nentOdes, 7591's, and some poiver triodes and, power tetrod,.-:. @ Condor Electronics bk, The tesfset measures up to four tubes at a tinc, and has a separate 125 North 36th Street test socket for short circuit testing. Separate ,selector SWitcheslor -- Seattle-WA 98103 Bias voltage; Plate voltage; Measirrement Functionrand..Test Socket '206 633 5190 206 633 0803 fax Select are pn;vided, along with protection fnseS,'Indicators and a mains switch. All measureMent data appear on a large3..5 digit LED display. •

Your online source for name brand audio tubes

Enjoy the convenience of purchasing audio tubes at our secure online vvebstore. We stock a wide range of products including Fi, Tesla/JJ, Svetlana, Sovtek, Sino, and JAN.

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Check out the selection at thetubestorescom

V ACU U M T UBE V ALLEY ISSUE I I

35 It's Like Music to Your Ears. Amperex Bugle Y audio tubes are back and they're eee1hen ever!

When it comes to sele ng premiutfpu o tubeeo your amplifier, accept no less than the est, Ampiere e Boy! Amperex Bugle Boy tubes are burned. in underfee oad with all voltages applied for 24 hours before t5einete ted fr noise 8- microphonics. The aging racks used are tfrdrn i2ngiial Amperex production line built in Holland decades ago.

Complete test results 7,aref.supplied wit each tube, including plate curr elscreen cuerréni, filament current, and total harmonic distortione (Ap ttherTlip measurement is performed using one of the finest speirum añalyzers available — the Hewlett Packard 3561 A. Matchifik irdpair's' quartets -ctets is available for all tubé types.

Special test requirenents? Not a proble. For a slight additional C:parge we will test and ntcL í,9ur specified operating Conditions.

Types avallable: 6DJ8/ECC88, 12AU7A/ECC82, 12AX7A/ECC83 and many %ore!

So if you haven't dealt ''ith a source capable of meeting your demands, caii us at 1-80 7TUBE USA or 630-208-2200 today for information 'dn additioral products and the worldwide locations nearest to yo Yoi7Il like what you hear!

APD is pleased to announce BLUENOTE Midas Dampers are the addition of Hammond now available, along with other quality audio accessories - Thinking about Manufacturing's complete line of Classic Transformers and such as, equipment isolators building your Enclosures to our product and CD/LP treatments. The own amplifier? offering. Call today for a Midas Dampers (as reviewed Call 1-800- Hammond catalog or down load in Stereophile Magazine, February, TUBE USA it from our WEB site at 1996) are made of the highest w w w.tubes-r-us.co m/ quality materials available. classic.html. They reduce microphonics in your preamp tubes thereby enhancing the music you hear.

Call (I-800-TUBE USA or 1-800-882-3872 today for your copy of our

NEW A.PD 'brochurel featuring Audio Tubes, BLUENOTE and Ham mond products.

40W267 KesIinger Road P.O. Box 393 Richardson Audio Product Dhrision LaFox, IL 60147-0393 AP (630) 208-2200 Electronics (800) 882-3872 é a division of Richardson Electronics, Ltd. Engineered Solutions

You can also visit our Classic Components site on the Internet at: vvvvw.tubes-r-us.com

3 6 Back Issues, G oodies, lit Subscriptions

VTV #1 Spring 1995 $8 US - $10 Foreign Vintage Hi-Fi Spotter's Guide-Volume 1 Vintage Dynaco Tube Equipment - 1955-77 Over 450 photos & specifications of tube audio gear r

History and Testing of the 12AX7/ECC83 dual triode from the Golden Age of Hi Fi. 86 pp. $18.95 SPO TTER'S LU G . Tube Testing Methods + Early Amplification and Amps Vintage Hi-Fi Spotter's Guide Volume 2 g Volume 2 covers equipment not listed in Volume 1. VTV #2 Fall 1995 $12 US - $15 Foreign Almost 500 amps, preamps, tuners, etc are depicted. VINTAGE Heathkit - The Tube Williamson Years 1950-61 Edition covers early audio and includes a Speaker section EL34/6CA7 History, Types and Tests with most vintage manufacturers. 88 pp. $18.95 SPOTTER'S GUIDE Magnum SE EL509 Amplifier Project by Dave Wolze 1927-34 Western Electric Theater Sound Systems Vintage Hi-Fi and Audio Price Guide 1999-2000 Updated price & grading guide for almost 1,000 vintage VTV #3 Winter 1995/96 $12 US - $15 Foreign VINTAGE al- n hi fi amps, preamps and tuners. Includes Vintage pro PRICE GUIDE Eico Mono Tube Gear - 1955-62 audio and theater gear. Also, pro loudspeakers, N.O.S. Altec Lansing 604 Coaxial Loudspeaker History vacuum tubes and audio transformers. $20.00 Western Electric 300B History and Listening Tests 300B SE Transformer Listening Tests "Vintage Hi-Fi The Golden Era Video" 44. It Nià A one-of-a kind video covering the classic post-war and VTV #4 Spring 1996 $12 US - $15 Foreign 1950s home hi fi era. Over 80 classic audio amps, pre- 6L6 History, Types and Listening Tests amps tuners, are shown. This video is professionally pro- Vintage Bookshelf Speakers 1955-1965 duced. 34 min VHS NTSC $20.00 Early FM Broadcasting History HK Citation I & II Amplifier History and Mods The Ultimate Tube Substitution Guide No tube electronics enthusiast should be without this VTV #5 Fall 1996 $12 US - $15 Foreign book. Over 10,000 tubes are listed on 240 pages includ- The Ultimate FM Tuner Shoot Out ing: audio, radio, transmitting, and special. Features an Red Bank Guided Missle Tubes for Hi-Fi audio tube section with tube evaluation. $29.95 The Birth of the Marantz 10B Choosing Rectifier Tubes for your Guitar Amplifier Vacuum Tube Valley T-Shirts Two Styles to Choose From! VTV #6 Winter 1997 $12 US - $15 Foreign A) VTV Marching Tubes -"Big Tone" Fisher 500 - History, Models and Restoration 1 sided available in Burgundy $15.00 XL only A Tribute to Avery Fisher by the Fisher Doctor 6550 and KT88 History, Types and Listening Tests B) VTV Tube Sunburst Shirt with 2-color black & orange Loftin-White Amplifier History by Alan Douglas - art as pictured plus large 2-color RCA tube diagram * exploded view on back. (Available in gray) $20.00 XL only VTV #7 Summer 1997 $12 US - $15 Foreign C) Official VTV Cap - High quality dark navy cap with silver 6DJ8 & Frame Grid Tubes + Listening Tests embroidered "Tube Head" on front. "Vacuum Tube Valley" Altec 1950s Theater Amps and Modifications stitched on back. Velcro size adjustment, 100% Cotton $20.00 The Great Voice - The Peter Jensen Story Computing with Tubes - The Savage Art 'ULIM VTV #9 Spring 1998 -Transmitting Uncle Eric's Tube Dumpster - 417A/5842 Tube Review, A_mpeg SVT Guitar Amp, Altec 287W amp, Bargain Vintage Hi-Fi VTV #8 Fall 1997 $12 US - $15 Foreign $12 US - $15 Foreign EL84 History, Types & Listening Tests RCA Tube Mfg at Harrison, New Jersey VTV#10 Summer/Fall 1998 200 watt OTL Amp Project by Allan Kimmel Story of the 6V6, Hi-Fi radio in the 30s, 300B Listening Tests: NOS and Vintage Types PP SV572 amp, Ultrapath Line Stage Bruce Moore Tube Audio Pioneer $12 US - $15 Foreign

Name Date Subscribe To Vacuum Tube Valley Address The Classic Electronics Journal City State Zip $36/year US - 4 issues $43/Canada, Please Send Me The Following Products $56/Europe & $66/Asia & World

VACUU M TUBE VALLEY Add $5.00 Shipping per order in USA / Add $10.00- Item Air Mail Foreign Shipping $ RO. Box 691 CA Residents Add 8.25% State Sales Tax (CA Tax) Belmont, California 94002 USA Phone (650) 631-6550 FAX (650) 654-2065 Credit Cards, U.S. Bank Checks or Money Orders OK TOTAL ORDER $ email - [email protected] Credit Card # Exp. Date Signature www.vacuumtube.com A LEGEND REBORN! The legendary British made KT66 is one of the most Enlarged, heavy gauge figured glass bottle handles higher temperatures, famous tubes of all time. In improving performance at higher the 60's it powered other power levels. British legends like Quad Hi Fi amps and the first Marshall Extra thick premium quality star mica guitar amps. This tube was spacers (top and Bottom) improves ' ',

performance stability and reduces e the sound of Eric Clapton on adverse microphonics. the classic John Mayall Bluesbreakers album. Precisely tensioned filaments for better mechanical stability and •e' reduced adverse microphonics. If you can even find an orig- inal KT66 today, they'll set Deep swaged heavy grid rods you back up to $300 made from pure copper provide A apiece. improved mechanical support for grid windings. Groove Tubes has given Brite nickel beam focusing elec- new life to this legend, trode concentrates the electron creating our own tooling to flow precisely on the plate for manufacture it again. We improved power output. were able to keep the Heavy duty plates made from a sound and improve on the special alloy are stiffened with tube in satisfying ways. ridges and coated for strength and durability. With our precision tooling

Enlarged phenolic base provides and modern manufacturing excellent contact with glass envelope processes, we consistently hold and insulation, preventing shorting le"' tolerances the 60's original could between critical components. never attain. Insights from our research allows us to control musical parameters no other All specifications equal or tube maker even knows about. exceed the original Genelex Gold Lion KT66 standards. Groove Tubes is offering Performance Matched Duets of the GT-KT66R @ $120 (U.S. retail price).

Groove Tubes... The American Tube Company, since 1979. 12866 Foothill Blvd., Sylmar California 91342 USA Tel: (818) 361-4500 • Fax: (818) 365-9884 • www.groovetubes.com

38 Purbcpor5 o ta55te Zran5tormer5 Sc Cntto5ure5

Single Ended, Push-Pull Filter Chokes and Potted Tube Output Transformers

LA »

Aluminum & Steel Chassis and Diecast Aluminum Enclosures

• Open & Enclosed Filament Transformers High Voltage Plate Transformers

Contact us for a free catalog & list of stocking distributors HAMMOND NUFACTUR

4700 Genesee St. - Cheektowaga, NY 14225 USA Phone: (716) 631-5700 Fax: (716) 631-1156 394 Edinburgh Rd., N. - Guelph, Ontario N1H 1E5 Canada Phone: (519) 822-2960 Fax: (519) 822-0715 www.hammondmfg.corn

39 Products by:

Allen Bradley Alps Caddock CAIG Labs Cardas DH Labs Elna Cerafine Hammond Holco Hovland MusiCaps Hubble Jensen Kimber Kable KR Enterprise LCR Caps Lowther Magnequest Mills MultiCap Neutrik Noble PFT Chassis Ram Labs Roederstein Solen Sorbothane Sovtek Svetlana Celebrating our 10th Anniversary 1988 - 1998 Tesla Our 1998 Catalog & Design Manual is now available featuring tons of kits, parts, Vampire books, software, schematics, fun projects and the usual info. It's just $12 U.S. WBT and Canada, $18 International, refundable. Visa and Mastercard Welcome. lborue labs Wima P.O. Box 260198 Littleton, CO 80126 USA and many more... tel: 303.470.6585 fax: 303.791.5783 e-mail: [email protected] website: http://www.welbornelabs.com

e are a proud dealer of Western Electric Audio Products. WThe current production 300B is now in stock. Electron Valve stocks a wide array of NOS Vintage Audio Tubes like Mullard EL34, RCA 2A3, and Mullard 5AR4. We also have a good stock of Old Production Your source for hard to find Western Electric tubes such as Vintage Audio Tubes 205B/D, 252A, 274B, 300B and many others. Electron Valve carries Precision Tested Ram Labs and Quality Vacuum Tube Reference Tubes. These tubes are computer tested, graded and matched to ultra high specifications predetermined by Roger A. Audio Components Modjeski. We also carry the Music Reference MR RM-10 (Push-Pull 6BQ5, 35W/Side) Stereo Amplifier and the Sieby out ehile to set a detailed look al all of our MAI& Music Reference RM-200 (Push-Pull 6550, wl,,,w.elecixenvalve.com • Email: [email protected] Phone: 901-382-9955 • Fax: 901-382-9956 100W/Side) Stereo Amplifier.

40 I.

aM9le

Svetlana ELECTR ON DEVICES

They made it first but

we made it affordable!

Svetlana is proud to introduce the

SV300B power triode. Recreating

the tonal qualities of the original,

the SV300B sets a new standard

of excellence. It is manufactured

in Russia under Svetlana 's

stringent quality control and offers

ultimate sound and appearance

without the high price of the

original. The SV300B is tested at

the factory and matched into pairs,

ensuring optimal performance

and durability.

8200 S. Memorial Parkway Huntsville, AL 35802 256-882-1344 • Fax: 256-880-8077

3000 Alpine Road Portola Valley, CA 94028 For an early review of the Svetlana SV300Bs sound, 650-233-0429 • Fax: 650-233-0439 see Vacuum Tube Valley magazine, issue 8. page 22-23.

Copyright 1998. Svetlana Electron Devices, Inc. All rights reserved. www.spetlana.com

41 "Deep Impact"

That's the effect our A-4 has on it's owners.

Fully Assembled $559.00 - Kit $449.00 - Chrome chassis add-on $95.00

• 30 Watts Per Channel • Extremely Low Noise • Tubes: 4/12AU7 & 4/EL-34 • Point To-Point Wiring • Exceptional Quality & Sound CI Ultra Linear Push-Pull

We carry other Amplifiers, Preamplifiers and Phono-Preamplifiers.

All kits come complete with step-by-step manuals, schematics and drawings. Call For Your Free Catalog!

Antique Sound USA Made in the USA

6717 NE 181' Street, Kenmore, WA 98028 USA Phone 425-481-8866 Fax 425-485-3836 E-Mail: [email protected] Web-site: www.amemura.com/sound/

42 Matched Pair WE300B

Inksiem Elidrric fit Fide> product.; pre marketed tuot ote by Mores non. Electnc ts rorodernork of Lucent> .ntogras Inc, Western Electric Audio Products AT&T d,noces, Inc., licetsted to Weenie Corp, a company mdeperedent of brunt. pfEell tobormeries Wesem gee* 1230 Peachtree Street • Suite 3750 • Atlanta, GA 30309-3575 •(404) 874-4400 fax (404) 874-441 5 High Fidelity products ore stored ifl -the U.S.A. e-mail: [email protected] • Internet: www.westernelectric.com If You're Looking for that Special Mix of New and Vintage Components for a Special Project, There's a Good Chance We have Everything You Need under One Roof.

Tubes • Transformers Capacitors • Resistors Books • Videos • Knobs Grill Cloth • Chokes Filament Transformers Tube Sockets • Project Chassis • Soldering Tools Switches • Speakers Decals • Rebuild Kits Replacement Dials • Test Equipment • Meters Spotters Guides Reproduction Manuals Paint • Tuning Capacitors Hats • Shirts

More Hardware Than You Would Believe

Phone (480) 820-5411 FAX (480) 820-4643 or (800) 706-6789 Visit our website at wwvv.tubesandrnore.com