Let the carnage begin!!
I also find that the rectifier used makes a BIG difference in what you're hearing. Some say, volts is volts, but the best argument I've heard is how the volts are created can have a a major impact on how the rest of the circuitry interacts. Same difference as you'd see changing a grid on a power tube ... electrons are electrons? With a rectifier, the operating characteristics of the tube design can and will change the linearity and response of the output tubes. Power draw and how many amps it takes to create the B+ can also shift the "sweet spot" of a design significantly. I suppose whether this affects what you're hearing depends on your equipment and listening habits.
Anyway - the Chinese 5AR4's don't sound bad, but don't hold up when compared to a NOS 1950's Mullard 5AR4. I also find the GZ68 copper cap to be harsh/pinched compared to either. None of them hold up to a Mullard GZ37 that's my daily driver.
Seems to me the biggest difference is that the 5AR4's are borderline capable on an ST120, especially trying to drive a quad of KT120's at 60mV. Right at the edge of browning out with high impact audio. The GZ37 doubles the max pass capacity of a 5AR4, so no worries about hitting the wall.
I also ran a Philips 5R4GYS for a bit and found that to be very capable with a quad of KT88's. Couldn't handle the KT120's at the higher bias though. Recently picked up a set of TAD KT88STR's and loving those, so I may try switching the Phillips back in and see what happens.
Worth repeating ... these results are with an ST120. Any of the big bottles I use would be ... problematic ... on a stock Dynaco without some serious upgrades.
PS ... haven't tried any of the "new" Mullards yet ... no big rush ... I'll wait till they've had a chance to establish a track record before biting.
Oh. I never ever run signal to the amp until it's had a few minutes warmup. I've also got mine set up for slow start which helps. It's also the last thing I turn on in the system - otherwise, the HTPC digital server can put a pretty good thump to the speakers when it boots. Best avoided.