Are you sure it is running balanced output into the transmitter?
Don't use phone jacks or RCA jacks.
If hum persists, try lifting the shield on your XLR connector.
73DG
Hmm I didn't think of that. I bought it as "un-tested" so I was just plugging into the phono jack and listening as a quick test. I think I can get an adapter to run it into one of my modern rigs and see if the hum is still there. By the way, have you gotten a chance to see if you have any of those caps?
73
William