I have a 251 that has low output. After it warms up a bit it starts a 60/120Hz hum. I don't have a sub 6072A tube to swap in real quick, but do have 12ax7's laying around? Would that help as a quick test? The 6072A tests just under "OKAY" on my BK 667 tube tester, but though subbing would be the best test.
Power supply seems to measure fine. 120Vdc and 6Vdc heaters.
Power supply seems to measure fine. 120Vdc and 6Vdc heaters.