[GrimJosef]

It's your call of course, but I wouldn't use a cryo-treated one. There are people who believe that they sound better, and belief is a very powerful thing. But it's hard to see how, objectively, this process can make any positive difference. And if the very unusual thermal stresses should happen to micro-crack the glass-to-metal seals that will weaken a valve which needs to be at the top of its game, so to speak.

My 'test' GZ34 is a Golden Dragon one which is cheap enough that I can afford to risk it (unlike the Mullards) yet robust enough that it's run for quite long periods in quite a few different amps, some of which had faults which might well have overloaded it. Of course I could just have been lucky with this one.

Cheers,

GJ