Marshall head volume up & down?

[mr. torture]

Hello, if my Marshall JCM800, while playing, has it's volume raise up and down all by itself what does it mean?

Power tube going?

Preamp tube going?

Help please :-(

 

[Farview]

Plug a cable from the effects send to the effects return. Sometimes the switching jack for the effects loop gets goofy.

If that doesn't do it, try new tubes.