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I'd check each preamp tube plate and cathode voltages to make sure they are getting proper values. After that, since both channels seem to be overdriven, I'd look at the shared input stages around IC1 and IC12. If those look ok, then I'd go to sheet 3 of the schematic where the clean and dirty come together again at FET18 and to the right.
Does plugging a signal into the effects return give a clean powerful sound? If so, then you can rule out from the effects loop return thru the power amp section.
Looking thru my notes on a Blackstar HT Stage 60, I had -46.2VDC on pin 5 when I was biasing (504V on pin 3) a set of EL34BHT tubes. Your TP13 bias supply voltage of -50V seems to be much less negative than you had before.
Does plugging a signal into the effects return give a clean powerful sound? If so, then you can rule out from the effects loop return thru the power amp section.
Looking thru my notes on a Blackstar HT Stage 60, I had -46.2VDC on pin 5 when I was biasing (504V on pin 3) a set of EL34BHT tubes. Your TP13 bias supply voltage of -50V seems to be much less negative than you had before.
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