Help with humming Eico HF20

[Wes_in_VA]

One of my HF20's has developed a 60Hz hum. It's been going on for a few months but I'm finally getting around to looking into it.
The pair of these were reworked to make them true power amps. Recapped and all that as part of the deal.

The hum is unaffected by adjusting the volume and it's there whether there's any input or not. It's barely audible when there's music playing and you'd have to be right up on the speaker to here it under the music.

When you turn on the amp, it takes the buzz a few seconds to start and when it first starts, it'd louder for a second or two and then subsides.

Any thoughts? I have no experience with repairing stuff like this but I'd be willing to take something on.

 

[gadget73]

Are you sure its 60 and not 120? 120 hz would be power supply related most likely.

Imbalanced output tubes can cause this. The fact that it quiets down some as it warms up makes me think thats what is going on. This would also tend to be 120 hz.

60hz could be something whacky in the hum balance circuit. Looks like R33 is the hum pot. Have you tried adjusthing that? Could also be that it died.