trouble with a Marshall Valvestate Vs 100 head

[Walter]

Hey guys,
I am new to this forum and haven't had a chance to fully explore the archives so I apologize if this has already been covered but here it goes....

I have a Marshall Valvestate vs 100 head and lately I have been noticing that after a minute or two of playing, regardless of what channel it is on, I get a temporary drop in volume. This happens seemingly randomly, sometimes it goes a while with nothing and some times it is every few minutes that it gets quiet for several seconds.
I can only assume that it is a prob with the input stage because it affects everything and not just one channel. I am sort of new at this so I am a bit lost but i did find the schematics that other ppl posted.

If anyone has any ideas please let me know.
Thanks again

[drewl]

Possible bad or loose solder connection, dirty jack or the 12AX7 is going bad.

[e_c_mccollum]

What a coincidence, I am repairing one now.

Check for bad solder joints. Remember, just because the outside looks good does'nt mean the solder joint is okay. Inspect the circuit board traces for cracks and board lifting.

If you need a schematic, ask twist.

[Enzo]

Check particularlt around the output jacks, and the headphones jack. And check the phoes jack cutout contacts, since they are th speaker return path to ground. Also try patching a cord from effects send to effects return jacks