cyro tubes

I've seen on the internet several tube dealers promoting cyro treated tubes. Anyone have any experience with them? Is the sound or durability any different? I have a Jolida 502p that I will be purchasing a back up set of tubes for and found the cyro idea interesting.
Hi Al2214

I have some new re-issue cryoed Ruby 12AX7 tubes and some NOS GE 5751 preamp tubes that were cryoed as well and I haven't heard any difference with their non-cryoed counterparts in my Jolida 502P amp. As for cryoed power tubes I never did any A/B testing between cryoed and non-cryoed. I do have some cryo treated Tung Sol KT-120s and they sounded great with the 502P and I haven't had issues with longevity.
Be careful - i purchased a pair of 12ax7 Mullards and a pair of EL34 Mullards and they acted very oddly (perhaps they needed extra burn-in, I don't know). On the other hand, I purchased a pair of gold pin Electro-Harmonix 5751's that are awesome. I'm using them in my phono stage to pare down its agressiveness, with great result.
Cryogenic International in Scottsdale, AZ can tell you all about this process; Charles does it for many tube dealers and manufacturers. It improves the gas molecular structure and lowers the noise in them.