Thanks....I have a YBA-1 bassmaster, which doesn't have an adjustable bias pot, but Tesla EL-34s do fine when tested (with a bias probe device), drawing 32 mA and sounding fine. So I leave that amp completely stock.
The YBA-1A Mk II bassmaster is the one I'm more concerned with, as it has higher plate and screen voltages, to put out ~ 80 watts from 2 power tubes (originally American 6CA7s back in the 70s). Fortunately, it has a bias 'wiper', and with the Teslas I can adjust for a current draw of 34 mA & it sounds great. I think the wiper is turned all the way to one side for that value, ie, I could adjust it for higher current if needed, but not lower).
I'm just curious if you had to install a bias part in a YBA-1 amp to take the KT77s. Or if anyone has a YBA-1A Mk II, if the adjustable bias wiper didn't allow for a workable current draw.
(Btw, I subscribe to Aiken's view ('the last word on bias') on bias - how it's mostly to avoid obvious over-bias (where it sounds lousy), and obvious under-bias (where the plates are getting that subtle red glow). In between is a wide range where it all sounds good, so I tend to go with the lowest current draw that sounds good - usually high 20s to lower 30s). thanks!
I find the JJ KT77 sounds best when slightly red-plating. I keep a strong set in for jamming and a weaker set that begins to glow for recording. Tubes can sound best when they are about to die!