Cryogenic treatment of tubes? Anyone with experience positive or negative?

I bought 2 pairs of Mullard NOS 12au7 (CV4003), one set cryoed and the other pair not cryoed.  I will be dammed if I could tell a difference.  Incidentally, one of the cryoed tubes started making noise right after the 90 day return policy ended.  I too got them from Upscale.

I've tried 3 or 4 diff. sets of cryoed tubes in the past and also after very careful comparison I really couldn't tell any difference either.One set of Mullard reissue el34 went fuzzy and noisy in a 2 month period and one tube went completely bad.

Maybe other people have had better experiences with cryoed tubes but I would'nt recommend them.

Kenny.

I have a Cryoset pair of Tungsol reissue 12ax7 that got a bit noisy after a month of use.  A standard pair was supplied with my Jolida amp and there seems to be no difference between them other than the standard pair did not get noisy.

The idea of Cryo'ing the tubes is to relax the metal parts to allow the  shapes to settle sort of it also improves  the electrical properties including less electrical resistance . similarly NOS tubes that have been sitting for a long time  don't need this because they have naturally relaxed over time. if the parts were already from old metal let say then you wont get as good of a change with the treatment. Some metals react differently as well so you get various results. if its cheep then its worth it, if done right, if not done right it can actually damage the tube and reduce the life of the tube. best way is to stick the tubes on a shelf for 50 years, oh that's NOS.