Tube Characterization: 6DJ8, 6922, 7308, CCa, etc


Does anyone agree with me that there should be detailed descriptions of the sonic characteristics of each of the popular versions of each of the above tubes. I've read Joe's Tube Lore and a number of manufacturers web-sites which are great general direction guides but they really don't tell us what we need to know in specific and defined terms. Perhaps starting with an overall sonic characteristic like liquid, or warm, or dry or transparent then their response at the frequency extremes (since this is always an issue with tubes), then perhaps individual characteristis with say female voice, piano etc. and then imaging. We would all purchase a set of cheap base line tubes that are known for consistancy and have clearly defined caharacteristics so that comparisons could be made to this benchmark. Then use benchmark recordings. Even better if we had the same equipment best yet if we benchmarked every component in the chain but not necessary because we would be dealing in relatve values.

Of course there is the question of synergy with existing equipment and the fact that we all don't hear exactly the same and so on and so forth, but again, it would all be relative. "Tube "A" has has better defined bass than the benchmark by a factor of 3 on a scale of 1-10 IMO" for instance. Of course this wouldn't be an exact science but it would give us real direction and be more useful than "this is a really great tube or this is a really, really great tube" or slavishly depending on the opinion of the tube specialty store who may be as honest as the day is long but does have to move what he has in stock. If we can bring this evaluation process closer to science we could spend less time playing this silly expensive guessing games and spend more time exploring the kind of sound we like and buying the kind of sound we want (not to mention, listening to more music) Thoughts?
anacrusis
Tvad and Neebee, there is no doubt that I support my design decisions !! :)

-And the reason that I made those decisions is based on the experience that I had with the tube types I mentioned. The 6DJ8 was a popular intrumentation tube (look in an old Tektronix scope sometime) and is very good in that application. Unfortunatly, the tube was not originally intended for audio and while it is very linear, it has a micorphonic tendancy that is profound relative to other tubes.

Despite that it has been popular in audio for a long time. However if one pays attention to what it and other tubes do, it will be seen that any equipment that uses it will have a coloration particular to that tube- you all know what I am talking about. The fact of the matter is that audio (high end anyway) equipment ought to have *no coloration at all* so if you want that you will have to start with a less troublesome tube. It really is that simple.

I was influenced to try the 6SN7 after seeing the the MFA Luminescence preamp (which was extraordinary in its day) as well as the Vacuum Tube Research Labs stuff. It was easy to discern why the tube had/has a serious following.

So I was just letting you in on what I have found to be true over the years (I think most of the more respected people posting here do exactly the same). I hope this is not troublesome.
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Ah- OK. The 6SN7 will *generally* offer you smoother sound with less 'hash', especially at higher volume levels where airbourne vibration can affect the tubes. Detail will be the same and 6SN7s will generally allow you more drive ability as they will handle higher currents better than 6DJ8s. Lifespan seems better too. The 6SN7 will make less gain, but often that is not an issue in driver circuits, line sections or DAC outputs.

Another way to describe the difference is that circuits with 6SN7s sound more refined, while those with 6DJ8s sound more brash.
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gentlemen:

how can a statement regarding the sonic characteristic of atube be independent of a tube circuit ?

not all 6sn7 tubes sound the same and not all 6 volt tubes sound the same, provided a tube circuit is tube sensitive.

there is sufficient variation within tube class to render a generalization stating a "generic" tube sound not a good basis for selecting a component.