After some weeks of successful use, I had a strange noise coming from one channel (sometimes sort of a whistle, other times an intermittent crackling sound) - traded out the driver tube for a new one, no change - traded out the output tube and it was silent again. Left the amp on a few minutes with some test speakers to be sure everything was OK before putting it back in the system and suddenly it started smoking. The cathode resistors in the channel that was noisy (R16 a, b, c) burned big time - board delaminated, adjacent coupling cap sort of melted on exterior.
Greatly appreciate anybody's idea as to what might have happened? Or where to look? Thanks very much!
Charlie