John P Lloyd
I have tried it on 3 power supplies, in fact. One on my workbench (a switcher) and the other two are 50 amp astron's that I use everyday in the shack.
I always troubleshoot into a dummy load with a watt meter in line.
Putting it on an antenna has the same result with the hum.
The voltage from the PS's is 13.8.
I'm going to look into it a bit more this weekend, and let you know if I come up with anything, especially about the power output.
Thanks for replying!