The B-3 and L-07CII are a very nice match. When driving some APM-77,and sourced by a Sony CDP-R3, it's pure sonic nirvana
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Ah, those dual volume pots per channel, opposite interacting... made me confused at first, and still makes no sense to me why one at the back and one on the front... Anyway, I've put both at no attenuation at all. That's why mankind has invented pre-amps after all...I think... And as such the standard quality carbon pots have the least sonic influence on the signal.
For the moment I run the B-3 on AC input because the L-07CII desperately needs a recap, now having a naughty DC offset on one channel, tripping the B-3 into protection if connected in DC. Still..... it sounds great
The power rails to the VFETs are at ~42.5V . Say 45V max with 7% mains increase. Hence, 63V rated buffer caps are the thing to go for. 50V would also be ok, but leaves little margin and shorter lifespan.
EDIT: it is probably not required to replace those extra large PSU caps; they are most often still in excellent shape. But as I mentioned before, the amp needed months of daily playing to start sounding well. Bigger caps means longer reforming time.