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Do vacuum tube test values reflect sound quality?

I recently ordered a pair of output tubes to try in my LTA MicroZOTL preamp. Two Sylvania 6SN7WGT tubes, Gold Brand. I’ve had good luck with Sylvania 12sn7gt bad boy tubes, so I thought I’d give them a try.

After I bought them, I saw a similar pair for more money that had slightly higher test values. Does that mean they might sound better or that they just have more life left? What properties do you look for in tubes?

Below are the values of the tubes that I bought.

 

Tubes are matched for dynamic gain and structure, testing at 3000-2750 and 3000-2750 where pass/fail is 1625 micromho. They have the same structure inside and out, having matching date codes of "922", the 22nd week of 1959

sls883
lewm
13,447 posts
 

For a cathode follower you WANT high transconductance. Tubes like the 12AX7, used by many companies as a cathode follower, are not a good choice. They do it because there are billions of 12AX7s in the world, and more are being made in Eastern Europe. The CF changes voltage to current. 12AX7s are puny for current. 

sls883 OP
669 posts
 

@donavabdear LOL.  I'm probably close to 30. 

I have ten 6922 tubes that I bought for a c-j preamp that ended up having issues and I returned it.  Found a set that liked (four + 1 extra), so I bought five more.  I don't have anything that uses 6922 tubes. 

curiousjim's avatar
curiousjim
5,071 posts
 

I have pondered this myself, but I really don’t have a clue.  My only  experience has been that there’s a noticeable difference between mismatched tubes. 

I kinda wish I could have bought a tube tester 40-50 years ago. 
 

donavabdear's avatar
donavabdear
516 posts
 

@sls883
Brother I hate tubes like I hated that girl in high school that I could never stay away from. I know they are wrong for me but they are so good. 
I bought some hybrid tube amps BHK 300s  which have a tube front end that makes sense to me but still there is the inevitable degradation that happens with tubes even if they test perfectly. It's like the frog in the pan of water it can't tell how hot it is before it boils. 

 

lewm
13,447 posts
 

In a well designed circuit, tubes will last quite a long time, certainly many years, sometimes more than a decade. One of the few good uses for a tube tester (and I specify a tester that measures transconductance in units rather than as “good” or “bad”) is to record the values for Gm when new and then retest the tubes periodically if you want to ameliorate your anxieties about tube aging. Hickok made the best testers and they all can measure Gm, for example. Should one prefer SS because of tubes aging? With SS you get sudden total failures where the discrete transistor or integrated circuit that failed is no longer available. Nor is there anyone left with expertise to do the repair. With tubes you just plug in a new one.

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