The spike protection diodes in this amp had shorted so it was blowing fuses. Unfortunately, the 7027s were all bad, so I installed some SED 6L6GCs, which are electrically equivalent but not quite as tough. I decreased the bias to reduce plate voltage as much as possible, and increased the value of the screen grid stoppers.
I also replaced the master volume (installed by a previous tech) with a post-phase-inverter type and installed new electrolytic capacitors.
