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Tube Characterization: 6DJ8, 6922, 7308 Part II

This is a continuation of the thread:
Tube Characterization: 6DJ8, 6922, 7308, CCa, etc

This above thread was dense with information regarding tube selection, classification and characterization but like many threads, branched off into more specific areas of focus. Though I would definitely refer to this original thread as a point of reference, what I would like to do here is condense much of the information specific to it's original intention. The objective evaluation of 6Dj8 family of tubes.

One of the most thoughtful responses and one for which I am most grateful is:
My advice if you are tube rolling is to be careful about documenting what you are doing, and make sure you can return tubes that you buy from NOS/antique dealers! *Above all* remember that you are supposed to be having fun and don't go off the deep end. Its not pretty
To this end I have decided to cool my jets a little and take a more moderate approach.

The questions are:
1) Can a tube within an audio component be evaluated for its sonic qualities or will the associated circuitry be so influential on the sound that such an evaluation would be pointless unless put into a specific context (ie the same preamp)

2) Will a tube retain enough of its sonic signature with specific components or specific circuits to make such an evaluation fruitful?

3) Is there an objective language or terminology that we can use which will make such an evalutaion comprehensible?

Many of the most experienced audiophiles in this forum feel that it can not be done, at least meaningfully. A number of others feel reservedly that it can and a few are of the opinion "let's give it a go". Some just find pleasure in trying out different brands on a casual basis(a very sane point of view imo).

Some contributers feel and for good reason that the manufacturer used certain tubes for good reason and that tube rolling would just be making trade-offs. If you want a different sound, buy a different preamp, cd player, what have you.

Before anyone undertakes such a study they should refer to the existing information contained in "Joe's Tube Lore", and evaluations done by Vintage Tube Sevices, VAC, and Vacuum Tube Valley, especailly issue #7 (thanks to Jab and Rchau). Consider that some components are just more sensitive to tube changes than others. Lastly, be sure that you can return, at least exchange tubes for

One comment by Atmasphere I found particulary interesting was his assertion that:
If you are dealing with the best of the best in all tube types you will find them all very close.
and also adds that the 6SN7 series of tube is iherently better than the 6DJ8 series and to me supports the idea of just changing preamps. By the way Raymond Chowkwanyun of enjoythemusic does a capsule review of this tube type: http://www.enjoythemusic.com/magazine/equipment/0304/6sn7.htm

There is also a strong contingent of contributers that feel nos tubes are inherently better sounding than nns tubes. At the prices some old stock tubes are going for I find it difficult to believe that a modern tube manufacturer can't duplicate or even improve construction methods producing superior tubes and still make a nice profit but that so far does not seem to be the case.

Imin2u, if you are still interested, may I suggest starting with some of those tubes you have that haven't otherwise been reviewed and we can start putting them through their paces. We can move from there to confirming existing findings.

I invite anyone who would like to be a part of this experiment to tell us a little about the sound your favorite 6DJ8, what you use it in and if you'd be willing to run other tubes through your system.
anacrusis
tvad
9,467 posts
 
Look for Siemens & Halske CCa made in the early 60s, identifiable by their grey mica supports versus shiny metal supports. Siemens & Rohre CCa were manufactured later.

The best Amperex and Phillips tubes were made in the Herleen, Holland factory. I have never owned any from the late 50s, but all the tubes I have owned from these brands made during the 60s have sounded essentially the same (given the same brand and tube type).

I prefer Mullards made in the Blackburn, UK plant. They have a slightly warmer and more refined sound than their Mitcham, UK counterparts, which in my opinion sound closer to Amperex or Phillips tubes. Can't explain why this is so, but for me it just is.
anacrusis OP
69 posts
 
tubes really do an amazing job at screwing with the signal when used in the pre and main stages

I would tend to agree with Dave b that tubes are doing something to the signal but then again, who cares? They sound so good and impart an almost indescribable life to the sound. Stop and listen right now to the ambient sounds around you, are they liquid or tube like? Not to me. There is an almost gray or white background and no warmth whatsoever. There is an immediacy and potential for power delivery so ineffable that it cannot be described. There is no place from which to take a point of view. There is no place to hide.

In many ways amplifiers like the Plinius SA-100 Mk III do a good job at approaching reality and the best, almost uncanny experience I have ever had with recorded sound was hearing the Weavers at Carnegie Hall through SAE separates. SAE is IMO the prototypical solid state sounding amplifier. I've heard this recording through many other systems and nothing even came close. Curiosly the recording was made with tubes, so maybe there is something to tubes at the source.

anacrusis OP
69 posts
 
Thanks Tvad! You are really bringing things into focus. Still, I'm a bit confused about the Amperex PQ deal. Is PQ comparable to a 7308 or do they have 7308s that are not PQ? Where do you reach diminishing returns?
jafox
1,348 posts
 
Anacrusis, the issue of tubes is not only about tonality. Sit at a piano and hit a few keys. Do the notes abruptly truncate or do they gradually decay? Then listen to piano music through your favorite ss and tube phono stage, line stage and amplifier...even DAC. My listening observations over the years indicates that the ss devices do more to screw up the signal in this regard than do the tubes. The ss devices simply destroy the fundamental characteristics of the piano. Repeat this process with saxaphone and vocal music. The results are the same.
tvad
9,467 posts
 
To my knowledge, there is no 7308 that is not PQ.

Here is some required reading about 6DJ8 tubes from Brent Jesse Tubes.

Anacrusis, I say this with intended positive reinforcement and encouragement. It would be beneficial for you to do some additional research and reading about the 6DJ8 tube family. Each 6DJ8 variant has well published differences…leading to the path of scientific quantification you desire. Joe’s Tube Lore takes these differences into consideration. Once you have a little better understanding of the design differences and goals of the 6DJ8, 6822 and 7308 tubes, then take another read through Joe’s descriptions and try to correlate his observations to similarly designed tubes. I believe you might see more germane and less haphazard information in his descriptions than you originally thought.

When you ask about diminishing returns, what criteria are you using? Tube life? Tube quality, i.e. consistency from tube to tube? Their ruggedness and performance in radio and radar applications for which they were originally designed? Or, are you discussing high end audio application? Because if you are discussing audiophile application, then it comes down to personal preference. Many people prefer 6DJ8 tubes to 7308 tubes despite the higher quality production tolerances of the 7308. Others prefer something else again, which is why I have debated that the viability of your quest for a quantified, one-tube-only-for-a-given-circuit is unrealistic as it applies to high end audio.
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