juls, andy, nasabi nyo na eh.
i take rectifier change with a grain of salt. tulad ng mga nasabi na, you change the recitier to a different one, you alter the operating point, hence changing the sound.
if you want to have a solid change in your amp, change the output transformer. my 45 was ok with a local transformer with U.S. core, but after replacing it with a tamura, ibang usapan na. also the driver tubes can bring more sonic improvement/change as well as the power tube. ingat lang sa substitue, like a lot of people subs a 5693 to a 12AU7 not knowing na 150 V lang max Vp nun. kung sa foreplay na pre-amp pwede pero sa ibang circuit sunog yang tube na yan.
and as s2kov pointed out, tubes are matibay, i have my Sovtek 2A3 configured with a B+ 20% over the dissipation buhay pa din, pero hindi ko gagawin yun kung RCA na 2A3 noh.