Radio Hum

Hi Brian. The radio signal you receive has zip to do with your tuner. Something in your system is acting as an antenna.

Wondering if there are unused inputs on your preamp? If so I'd try using shorting plugs on those inputs. Just might be a cure.

Here's a picture of a shorting plug and also a place to purchase them.
Shorting plugs

All the tubes have now been replaced, a solder ground repaired, and a blown cap replaced. On a reference system, the preamp is now silent. I bought a new, shielded power cord. My amps were just cleaned and serviced by c-j. The major right side hum is gone. But there is still hum, which is much softer, and is now volume-dependent. And I still hear the radio. Even when I unplug my tuner entirely and there are no other radios around. Any other ideas?

Go inside your preamp and swap the tubes. If the problem moves to the other channel after the switch, you have a bad tube.

Thanks for the response.

I have connected the right preamp output to the other monoblock (call it left), and the hum follows it. Connecting the left preamp output to the original monoblock (call it right) results in no hum. So it is not the amps.

I have switched the left and right speaker wires, and the hum remains in the speaker connected to the monoblock connected to the right channel. So not the speakers.

I have switched the interconnects with each other and with different one with no change. Not the interconnects.

I suspect though you may be correct on a ground problem in the preamp right output, and I am looking into that.

To rule out the problem is the right channel monoblock plug the interconnect from the left channel of the preamp into the right channel input of the amp.

No hum/buzz the amp is ok.

You said you tried a different interconnect on the right channel, correct?

The loud hum/buzz/radio station could be caused by an open signal ground connection on the output side of the right channel of the preamp. An open ground at the input of an IC could cause the same problem. (The ground return could be broken on the outer shell of the IC plug at the preamp output end.)