Mesa Studio .22 Tech help needed...

[Chuckracer]

I have a first generation Studio .22 with the strangest problem. When I play a note, I can hear what sounds to me like 60 cycle hum beneath the note. It's most noticable playing higher notes and sustaining them. It's ONLY when the string is plucked.
I've changed speakers, bought new tubes, used several guitars, and moved across the country to no avail. It's not a grounding problem.
Any thoughts?

 

[John Phillips]

Filter caps, almost certainly. That amp must be over twenty years old now - which is the commonly-accepted 'life expectancy' for them, although there is no hard and fast rule.

 

[Chuckracer]

I changed the caps to no avail.
So I fixed it by buying another one.

 

[RussB]

Did you sell the "hummer"?

Did you buy another one?

Also, did you try inserting a guitar cord into the effects send & return (completeing the effects loop, sans effects)

My 22+ had a bad jack, that caused a bad hum...

 

[Chuckracer]

I still have the "Hummer" (nice nickname!), but I will be selling it. The "new' one isn't here yet.

I haven't tried the effects loop jump. I'll try that today. Thanks!