Here's an old story about 12AX7s that you might not have heard - it goes back to the second (?) VSAC, somewhere in the late 90s (?).
My late friend Tim Lollar (brother of the excellent boutique guitar pickup maker Jason Lollar) built a preamp with sockets for something like ten different tubes, switch selectable. All of them were on all the time to eliminate warmup effect, and each was operated at its own optimal current, giving identical normalized operating points. So we could pretty much count on technically identical operation, leaving only tube and gain differences. We adjusted the gain for identical outputs.
We did a mass listening comparison at the show with a crowd of about 35 people, each filling out their own rating sheet. The tubes were not identified until the session was over, and I as speaker did not know in what order Time was switching them. As close to a double-blind comparison as we could manage. No discussion was permitted until we had gone through all the tubes - of course, a pretty lively discussion followed (and carried over to the bar after)!
The interesting thing was, in the discussion nobody liked the 12AX7, and hardly anyone even mentioned it. IIRC, 6SN7s and 01A's were highly regarded, with a smattering of several others. Several months later, I tried to make statistical sense of the ratings. First place was all over the map. BUT ... for a clear majority, the 12AX7 was their second-favorite. I guess it was a little too politically-incorrect among audiophiles at the time, probably because it's a guitar tube. But in blind listening, it was very popular. I never found any other statistically-meaningful result from the test, and we never published the results. But I do tell the story now and then... :^)
