Cheers Anthony. Very helpful. Let me dig into that together with the other suggestions in this thread. I may also ask Nic P what suggestions he has for this amp. In any event, judging from the date code, the existing E88CC looks like originals he put in when building the amp.
Small unrelated question if I may? Absent an expensive valve tester is there any reasonable way to judge if a valve is going out of spec? I'm thinking of output valves here (EL34, KT88). Perhaps simply if it is getting to the limits of its bias adjustment? But would prefer judging things away from an amp.
cheers
E