My only problem right now is that the bias doesn't want to stay stable. It seems to be more unstable on the left channel, and goes to between .35 and up to .48 volts, and the right side seems to fluctuate between about .37 and about .42 volts. Each time I check it it seems to be different. I usually just check and don't change anything, let the amp play for another half hour, then check again, etc and it'll be off even more. Then I'll set the bias back to .4V on all tubes after having it fully warmed up, and it stays for a short while. Then after an hour or so, back off by a bit.
I can generally tell that it needs to be rebiased when it starts to lose its magic superfluous sound... my motto lately is "if it doesn't sound perfect, check the bias" and bam, usually that's the issue. Once I match them up again it really does come back into perfection zone and sounds great.
Any ideas or similar experiences? How stable is it supposed to be? Is this possibly just one bad tube ruining it for the rest? Thanks!