Julia said:
but I've had power tubes die in less than 10 hrs. with the bias set properly.
if a tube doesn't fail within the first say 3 weeks, it'll be good for a year or longer. At about 3 yrs you'll start seeing frequent failures again.
Try the input valve, the loop valve, then the PI. If none of those make a difference, then put in your old power tubes unless a major failure was the reason you changed them. If the amp works with the old tubes, then it was the tubes and you need to take advantage of the warranty period on teh tubes.
Yeah but going "dull and muddy' isn't really failing is it?
Maybe I'm too ignorant on this, only thing I've had happen with powertubes is I blew a few the other night which were damaged by a different broken amp..
But yeah, like I said I'd check all non-module preamptubes first, since that's very easy to do.
Also fig's comment is good: try plugging in directly without cables/pedals etc.
There might be something else in the chain screwing up your signal.