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 amplifier 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 triode 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 Capacitors 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 Vacuum Tube 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" battery. Marathon, Sovereign, By Eric Barbour Cardon/Sparton and Arcturus made simi- lar triodes 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 3 6 S N 7 : D RI V E R O F C H O I C E 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.