[ccomer1955]

I gave it a try last night. Cleaned out all of the tube sockets and each tube pin. I took the 7C6 from the 41-285 and swapped it with the one in the 41-280. And...partial success. The hum isn't gone entirely, but it is much less noticeable.

I found a crack in the speaker cone I had not noticed before, so I patched it. With my finger on the crack gently, the distortion seems to be less noticeable, too, so maybe I'm on the way. I should have the cabinet re-veneered by next week, so I'd like for the chassis to be ready to go by then.

Maybe I'll get a new 7C6 and take it outside to try. My house is an electronically noisy house. ALL of my radios have noisy tuning above 1100. An all electric community.