@georgehifi as you said, the bias can change the heat. that is why PrimaLuna has a "self-bias" to not run the tubes as hot. we can argue over specifics, but it is the essentially the same concept, of ultimately, how hard the tubes are run. The bias of any amp will effect the tube heat, not just PL. it is the manufacturers call for self-biased units, but the owners call if manually biased. In any case, it is true that tubes will live different number of hours, eg 5k vs10k, depending on the supportive electronics/bias adjustments.
@tubegroover @georgehifi . sending your USED tubes in to be cryo'ed may not show clear difference in sound. this is b/c "cryo'ing" tubes essentially hardens some metal structures of the tubes. these structures, metal pieces, etc will harden over time anyway with use.
So there would be a bigger difference b/w 2 NEW sets of tubes, one Cryoed and one NON-cryoed. But if you are sending in used tubes for cryo'ing, I would ask:
how many hours do they have on them? what is their expected life span in the particular amp you are using? eg, if a used tube has 4000 hours on it, and the life expectancy is 5000 hours, then it will already have been "broken in", in terms of the metal structures hardening. Sending it in to be crayoned with 4k hours would not make a significant difference IMO.
