[R-390] OT: Humbug transformer

[Shoppa, Tim]

N4BUQ writes:
> I realize it's a long shot and I'm either stuck with the hum or
> replacing the transformer but just thought I'd ask.
> BTW, this is an open-frame style transformer.

Back in my transformer-rewinding youth, hum of this kind was supposed to  cured by varnishing everything into place.

If you have the pumps and equipment, vacuum impregnation is the best way to make sure the varnish gets into every nook and cranny. I never had anything that fancy! Second best was "dip and bake". If you know someone at a local motor rewinding shop, they can probably help you dip and bake.

Simply brushing on varnish is unlikely to do any good IME. Meaning I tried it and it didn't work.

Tim.