would a bad CAP do this????
maybe one of the 2 big caps is bad?
or one of the 600v 0.1uf caps
I think I read this some place, more likely to happen on the old stuff. but now that I read what your #3 amp is doing, it came to mind
you could also try the DIY site.
when the problem is found it will most likely be a moment....
on the bias circuit you need 2 of these....1N5352B 15V 5watt zenerwhat do you have in there now?what do you have on the High voltage side of things?stock diodes are 1N5399