A major stumbling block to the wide use of tubes, especially in consumer audio electronics, is the fact that most tube-equipped audio devices are made in the United States or Europe in small quantities, and tend to sell for high prices. A change in this situation may be presaged by the arrival in the high-end market of many low-cost amplifiers and preamps made in offshore factories. Firms such as Antique Sound USA Co., Seattle, Wash.; Alpha Audio Laboratory, Belmont, Calif.; and Jolida Inc., Annapolis Junction, Md., have recently begun to import low-cost amps and preamps made by Chinese or Taiwanese factories. In the tubed guitar-amplification world, imported Asian-made products have yet to make a significant impact, although most inexpensive solid-state amps are Asian-made and a few tube amps are being exported from China. New Sensor Corp., of New York City, imports a line of guitar amps built for it in the Reflector factory in Saratov, Russia--these "Sovtek" amps have proven to be popular and affordable.
Solid-state designers have long attempted to produce tube simulators, using solid-state analog circuits like diode clippers and compressors to produce transfer functions and distortion akin to those of tubed guitar amps. Although these products have attracted only a limited following to date, the recent appearance of solid-state amplifiers based on digital signal processing (DSP) and using physical modeling algorithms, has stirred some interest among serious musicians.
To quote Art Thompson, technical editor of Guitar Player magazine, San Mateo, Calif.: "Transistor amps have definitely come a long way towards their ultimate goal of sounding exactly like their tube-powered counterparts, but I think most pro players and industry people have realized that this is a futile objective...." As to the success of DSP guitar amps like the Line 6 products from Fast Forward Designs Inc., Culver City, Calif., Thompson said, "We've tested some impressive tube-simulation devices, and better ones are undoubtedly on the horizon."
In the professional audio market, the final frontier for vacuum tubes looks to be in the mixing console. This device is the heart of a working studio, serving as primary signal router, EQ and effects controller, and the tool to mix down multiple recorded channels to a stereo master music program. Mixers used in most studio settings are large and complex and often equipped with computer-controlled automated mix-down capability. Although expensive, large mixing desks are frequently based on low-cost op-amp ICs such as the 5534, and use electrolytic capacitors for coupling the audio signal from stage to stage.
Some recording engineers have found this scheme wanting, hence recent introductions of tubed mixers. Companies producing such mixers are Summit Audio, the UK's Manley Laboratories and TL Audio Ltd., the latter being the sole producer of full-size mixing consoles with tubes at this time. The market may expand in the future, as interest in audio-tube electronics grows.
The most interesting new development is the introduction since 1990 of new tube types specifically designed for audio applications. Russian, Slovakian, Serbian, and Chinese factories currently opt to imitate the popular audio tubes of past types, such as 6L6GC and 12AX7. Yet the market has been open to some new tube types not directly based on any U.S. or European tube or modifications thereof. These types have aroused some interest from original-equipment makers, even though they seldom fit existing equipment.
In the guitar and pro-audio markets, new versions of classic power tetrodes and pentodes include, from the JJ/Teslovak Co., Cadca, Slovakia, the KT88S and E34LS, which are modified and uprated in power dissipation rating from their KT88 and EL34 prototypes. New high-power triodes, such as the SV811/572 series and 3CX300A1, have been introduced by Svetlana. Even more than other fields, the high-end market has seen an explosion of power triodes: the VV30B and VV52B from KR Enterprise Co., Prague, Czech Republic; Svetlana's SV811/SV572 series; the AV30B SL and AV62B SL from AVVT Technologies, Prague, Czech Republic; and many versions of the 300B from two different factories in China, two in Russia, and one in Slovakia--not to mention the revival of Western Electric and its resumed manufacture of the original 300B.
The KT90 beam tetrode, made by Ei Electronic, Nis, Serbia, has proved so popular for audiophile amps that a Chinese factory has even introduced its own version. Also winning a following in high-end audio are some Russian tubes unknown in the West until recently, such as the 6C33C-B from Electronpribor Ulyanov, Ulyanovsk, Russia. More new types are expected to be introduced, and some out-of-production types will be reintroduced, over the next several years.
Vacuum tubes enjoy an unshakable position in the design of guitar amplification. Their use in the recording studio and in home audio often seems like a fad, but it has very old roots and is therefore unlikely to disappear overnight, as fads do. Technical reasons for the use of tube electronics in some applications look solid and are well-defended both by professional designers and by the users, who define and drive the marketplace. So long as musical tastes demand them, tubed audio equipment and replacement tubes will be produced well into the next century, and probably thereafter.
About the author
Eric Barbour has been an applications engineer with Svetlana Electron Devices Inc., Portola Valley, Calif., since July 1996. His work involves testing and characterizing new vacuum-tube types and constructing and testing amplifier circuitry for Svetlana audio and RF tubes. Earlier, he was a senior technician and then an engineer with the U.S. Department of Energy, Intelligent Electronics Co., and Dionex Corp.
A staff editor of Vacuum Tube Valley magazine, Sunnyvale, Calif., since its founding in 1995, he also contributes to Glass Audio magazine, Peterborough, N.H.
Well-written articles on the subjective and objective characteristics of tube audio electronics include: "Why tubes sound so good," by Doug Fearn, Pro Audio Review, January/February 1996, Vol. 2, no. 1, p. 15; "The grounded ear" Peter Sutheim's column in The Audio Amateur, Issue 3, 1980, p. 34; and "Tubes versus transistors-- Is there an audible difference?" by Russell O. Hamm in Journal Of the Audio Engineering Society, May 1973, Vol. 21, no. 4, p. 267 (reprinted in Glass Audio, Issue 4, 1992, p. 16 on).
An unusual approach to testing for distortion products in power amplifiers is taken in "Spectral contamination measurement," by Deane Jensen and Gary Sokolich, presented at the 85th AES Convention, 3-6 November 1988 (Audio Engineering Society, New York City, 1988). Spectral distortion products of transistor amplifiers are compared, along with those from a McIntosh MC-30 tube amplifier, whose spectral plot is quite different from those of solid-state amplifiers.
In professional recording, tube equipment is a small but growing field. Recent articles about it include: "Tube processors--The outboard renaissance," by Loren Alldrin, MIX magazine, May 1997, Vol. 21, no. 5, p. 108; "A reader's guide to vintage gear," by Fletcher, MIX, November 1996, p. 84; "Retro-Active," by Michael Molenda, Electronic Musician, June 1995, p. 36; "The retro movement," by Sue Sillitoe, Audio Media, November 1994, p. 48; and "The vacuum tube rides again," by Walter Sear, MIX, May 1994, p. 24.
Textbooks on professional audio equipment design using tubes are a quite recent phenomenon. The most useful include Principles of Power and The Ultimate Tone, by Kevin O'Connor (Power Press Publishing Co., London, Ont., Canada, 1996); Vacuum Tube Guitar And Bass Amplifier Theory, by Tino Zottola (self-published, 1997); and Dan Torres' Inside Tube Amps (Sparpco Inc., San Mateo, Calif., 1996). An unusual reference book, with hundreds of schematic diagrams for tube-based music equipment is Aspen Pittman's The Tube Amp Book, edition 5 (Groove Tubes Inc., Sylmar, Calif., 1995).
Suitable for novices is Beginner's Guide To Tube Audio Design, by Bruce Rozenblit (Audio Amateur Press, Peterborough, N.H., 1997). All the books are available from Antique Electronic Supply, 6221 S. Maple Ave., Tempe, AZ 85283.
A taste of the fascinating and obscure world of "boutique" guitar amplifiers is afforded by Art Thompson's "20 mule duel: we wrangle a herd of new boutique amps," in Guitar Player, February 1997, Vol. 31, no. 2, p.118.
Plenty of publications intensively cover vacuum-tube audio electronic design. Their emphasis is usually on hi-fi audio, although material about guitar amps and professional studio electronics appears regularly. English-language publications include Glass Audio (Box 176, Peterborough, NH 03458) and Vacuum Tube Valley (1095 E. Duane Ave., Suite 106, Sunnyvale CA 94086).
Magazines that concentrate on high-end audio design include Sound Practices (Box 180562, Austin, TX 78718), Ultra-High Fidelity (Box 158, Cheshunt, Herts., EN7 6UH, UK), and Valve (Box 2786, Poulsbo, WA 98370).
Non-English tube-audio publications include:
The Italian Audion (Piazza Madonna Aldobrandini 7, 50123 Firenze) and Costruire Hi-Fi (Via Toti 9, 20010 Bareggio, Italy).
The Japanese MJ Audio Technology (Seibundo Shinkosha Publishing Co., 13-7, Yayoicho 1-chome, Nakano-Ku, Tokyo 164, Japan).
The French Musique et Technique (Bureau de Depot 1050, Brussels 5, Belgium).
The German Hi-Fi Scene (Dufourstrasse 165, CH-8008 Zurich, Switzerland).