My Marshall JCM800 50W blue a fuse.
New2 fuse holds but one of the output EL34s is glowing red hot, but the other isn't. Amp works, but hums badly.
That's consistent with it drawing a lot mire current of course.
Question: the valves are biased by a single adjustable pot. Is it conceivable that anything else bar the valve itself has gone t*ts up?
As far as I can tell the grids are isolated from the previous stage DC by at least two capacitors, and so capacitor failure is unlikely.