Boogie 50 Caliber + problem

[sakafraka]

I have noticed a problem with my Boogie
When I play the high strings ( E,B,G) on the clean channel.
I get a ring ( like a chime) sound.

any ideas on what this problem is ?
thanks.....:confused:

[theelectic]

Sounds like a microphonic preamp tube.

[LHanson]

If it's a ring modulator kind of sound, it might be that the power supply caps need to be replaced. It is @ 25 years old, it's about due.

Cool amp. I have one.