[Bret L]

****ter:


wrote:
Could you provide me with a list of tubes that were specifically
designed for audio? I'm finding that very, very few of the tubes used
in audio circuits were designed with audio in mind.

TIA!

LoL!

Well, so far I find that unless an amp uses 6L6, EL34, 2A3 or a few WE
numbers, or 6BQ5 (or variants thereof) for outputs it ain't using
audio tubes, people!

And the signal tubes better be 6267, 6EU7, 5879 or ECC808 or a very
few others or they ain't using audio tubes, people!

None of the rectifier tubes were designed with audio in mind. Even
then the audio market was small potatoes compared to the industrial
market at large.

McIntosh and Marantz were the worst offenders using tubes like 6DJ8,
6CG7/6FQ7, 6550 and other NON-AUDIO tubes in their circuits.
Ironically they are among the most sought out by collectors.


"Designed for audio" means different things in different contexts,
i.e, whether one is talking about small signal or power tubes, and as
opposed to general purpose tubes or tubes specifically designed for
other purposes. In some cases tubes specifically designed for other
applications work quite well in audio applications and in others not
so well.

In the case of power tubes, specifically audio types differ from RF
output, TV horizontal deflection, and voltage regulator tubes in
several areas. Linearity is at a premium, plate caps are undesireable,
and operating the screen grid at close to full anode voltage is a
design simplifier. In the case of triodes, the mu or amplification
factor should be high enough for easy driving but low enough to permit
the range of voltage swing to stay well over ground. On the other hand
really rugged plate structures, desireable in pi-section coupled RF
amplifiers to permit tuning by plate color is not really needed.

The 6DJ8 was specifically designed to be operated in cascode and
works well in that application. It is not generally considered an
"audio tube" but works well in some audio circuits. The only Marantz
amplifier app is the not great sounding Model 9 AFAIK.

The 6550 was an audio tube and nothing but. Where you got that from I
have no idea.

In the case of rectifier tubes there never was any reason to design
one specifically for audio.

It's worth mentioning that the hi-fi market at its peak (the JFK/MM
era more or less) was indeed lucrative and many power and signal tubes
were specifically designed for those markets. Many of those specific
designs were never all that popular as they did little to improve on
the old standbys in the minds of designers.

Some very good audio products use tubes not designed for audio but so
do a lot of ****ty ones. And some using only purpose designed audio
tubes are pretty bad.

The best thing to do to determine what are "audio tubes" is to read a
tube manual. Unfortunately, tube audio does attract some illiterate
people, and others simply too stupid to make sense of the information
found therein. The next step is to study some classic circuits and
commentary thereon. Many good print references exist. However, the
same issue applies there too.