Up With Tubes
In the world of audio amplification, the transistor has been predominant
for many years. Before the transistor, we had vacuum tubes. Surely you remember
tubes? They were those big glass gizmos with the glowing filaments that are
still in heavy use throughout Russia and the Iron Curtain countries.
High-fidelity sound-"hi-fi"-is generally reckoned as having become a recognizable entity in 1948. Tube amplifiers in those days typically had power outputs of 10 to 15 watts, and that wasn't "per channel," friends, because all of our sound was monophonic. Around 1950-51, the first really high-fidelity amplifiers were introduced. There was the Brook amplifier, with 10and 30-watt models. These were triode amplifiers, using 2A3 tubes. Then came the McIntosh 15 and 20-watt amplifiers, and a bit later, the famous 50W-2, a 50-watt "brute," beloved of the power-mad "hi-fi nut" (as audio aficionados were called in those days). If I recall correctly, the McIntosh amplifiers used beam pentode tubes like the 6L6 and, later on, the KT-66.
Arguments raged between the triode and the beam pentode advocates, with the former claiming lower distortion for their amplifiers, and the latter stating their distortion was just as low, but with higher power. Along about 1955, the triode-design Marantz appeared, and from then on the McIntosh and Marantz power amplifiers were considered state-of-the-art.
The tube preamplifiers of those days were fairly primitive devices. For example, there were ongoing arguments about the "correct" curve for phono equalization, so the preamplifiers had to be able to switch between the NAB, LP, AES and several other curves.
Tone controls were very simple affairs, and, of course, there were no tape monitoring facilities.
At the peak of the tube era, in the late '50s, tube amplifiers had acquired considerable sophistication. In addition to the established 40-watt Marantz Model 9, and the 75-watt McIntosh, there were various modifications of the famous British Williamson amplifier circuit. Special transformers were offered for do-it-yourself builders--the Partridge Transformer Co. of England regularly advertised their products in Audio, and David Hafler's Ultralinear transformers were highly regarded. By this time there were tube receivers, but the heat generated by the tubes in the relatively confined spaces of a receiver caused reliability problems.
When the transistor came into general use in amplifiers, around 1961, it was hailed as a great technological advance over tubes. The transistor was very small, thus making amplifiers and preamplifiers more compact, to say nothing of its ideal suitability for receivers. It didn't require an output transformer, didn't require any fussy bias adjustments, didn't generate any heat, and had the potential for very high output power.
However, when the first transistor amplifiers appeared, many audiophiles felt that the transistor had some characteristics they didn't find very pleasing. In their opinion, those amplifiers had a coarse, grainy, over-bright and hard sound, and when clipping occurred, the most horrendous distortion was heard. While there was rapid improvement in transistor amplifiers, especially in ameliorating the harsh sounding qualities, many audiophiles were still not altogether pleased. Thus, the continuance of tube amplification was assured. Even with the ultra-clean, smooth sound of the best current transistor preamplifiers and amplifiers, there are many audiophiles still fiercely loyal to vacuum tube amplification.
Perhaps the most ardent groups championing tube preamplifiers and amplifiers are the various so-called underground hi-fi magazines and their readers. In their opinion, the modern vacuum tube preamplifier and amplifier designs of today are far smoother and much more musical than their transistorized counterparts.
Although it must be close to 20 years since a tube amplifier has warmed my listening room, I have to respect the advocacy of tube amplifier designs by people for whom I have a very high regard. Not having a closed mind, especially where audio is concerned, recently decided to listen to several modern tube components to find out why some audiophiles are so enamored of their sound.
Today's vacuum tube preamplifiers and amplifiers are the products of a number of small specialist companies.
Oddly, as the most "transistorized" country on earth, the United States is a major producer of tubed audio equipment, along with England and, of all places, Japan. Among those available in this country are tube amplifiers and preamplifiers from Audio Research, conrad-johnson, Esoteric Audio Re search, New York Audio Laboratories, Luxman, David Berning, Counterpoint, and Eidolon, to name just those which come immediately to my mind. Although there is some mid-priced tube equipment, much of it is high-priced. I decided to sample models from both categories, and so have been listening to a Counterpoint SA-3 tube preamplifier ($795) and the conrad-johnson Premier Three preamp ($2,850), as well as the conrad-johnson Premier One tube amplifier ($4,350), which delivers 200 watts per channel into 4, 8 or 16 ohms.
The Premier One is considered the ne plus ultra of tube amplifiers by the underground press; it's a 135-pound monster that is rack-mountable (provided the rack is strong enough!). The Counterpoint SA-3, by contrast, is a compact, slim-line design, thanks to horizontal mounting of the tubes. It uses one 6DJ8 dual triode tube per channel in its RIAA amplifier section, with no voltage feedback in or around this circuit. The line amplifier uses one 6DJ8, shared by the two channels. Today's designers of tube equipment utilize solid-state components when they can be of obvious advantage. Thus, the power supply has four 1 N4007 solid-state rectifiers, four Zener diodes, and several transistors to ensure steady voltage regulation.
The front panel has a 41-detent step control for level, a balance control, a program selector, and a tape-output defeat switch (to prevent possible signal interactions with the tape deck when it's not in use), but no tape monitor loop. There are power, mono/stereo, and muting switches. The power supply is outboard of the main chassis.
Even after many hours of use, this preamplifier never gets uncomfortably hot.
Signal-to-noise ratio (often a problem with tube equipment) was quite good, with just a small amount of hiss using medium-output phono cartridges and playing back at fairly loud levels. As to the sound, the most immediate reaction is to its smoothness, its impressive stage width and sense of depth, and open, airy transparency. While the warm sound is especially notable in the smooth reproduction of string tone, the transient response on percussion is still fast, although not quite as sharply etched as in the best transistor preamplifiers. I would say the Counterpoint SA-3 is very non-fatiguing and easy to listen to, and would probably be good to soften the sonic contours of some of the brighter-sounding transistor amplifiers. Listening to this unit, I can understand why it is so well regarded for its sheer, musical sound.
As to the conrad-johnson units, I have not yet fully explored their potential, and I want to describe the unique circuitry of these superb units. But that will have to wait for a column in the near future. For now, I can say that after listening to the conrad-johnsons' very high sound quality, I know why their musicality is so treasured by the underground magazines.
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(Source: Audio magazine, Dec. 1983; Bert Whyte )
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