[tym]

I played the set for 2.5 hours without any problems. I have now put the original 36 tube back in (after reflowing the solder on the top cap a second time) and will retest.

EDIT: I tested another 3+ hours with the original 36 tube and the only change in volume was when the station I was listening to reduced power at sunset.

Phew! It might finally be fixed!