As I, er...mentioned. B+ goes up as the load goes down. That can cause a certain amount of stress depending. No light means fuse and the rectifier diodes are probably shot. I fixed a '66 Showman which had 3 dead diodes ($0.22) and one of the original power caps was in backwards. B+ was 495V with AC at 118V.
Did you disconnect one of the speakers or run it at 4 ohms?
fender question
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