f50 combo - hum goes away when I thump it!

[dirk_benedict]

Hi - I have an F50 combo that I picked up used, with what I believe are the original tubes...amp is at least 5 years old. I use it frequently. Anyway, right now when I turn the amp on (after having it on standby) it hums (not a squeal or a hiss, but a very dull hum). But if I give the top of the amp a gentle thud the hum goes away and everything operates fine.

Does this sound like a tube issue?

 

[elvis]

Only one way to find out...

Swap preamp tubes around, and see if the hum goes away or changes. If not, put in new power tubes.

I had a '65 Deluxe reverb that had the exact symptom you describe. It was the capacitors. However, your amp is way too young for that to be an issue.