On Jun 22, 9:26*am, "Tio Pedro" wrote:
wrote in message

...
I’ve finished refurbishing a Heathkit SB-401 transmitter, but have one
last problem to fix: 60 Hz tunable hum audible on the output.

If it is "tunable" hum, heard only locally, why are you worried about
it? That is being generated in the receiver, not the transmitter. Do
distant stations hear the hum? *That is the question.

Sorry, I wasn't clear. When I listen to the SB-401 transmitter on a
shortwave receiver, I hear hum modulation. The SB-301 receiver, which
drives the SB-401, works fine.

-Dave Drumheller, K3WQ