Odd volume problems with Marshall VS102R
Well ive just taken the opportunity to turn up my amp slightly since no one was in the house for a couple of hours.
The amp is a Marshall Valvestate VS102R (100W 2x12 Combo), and ive owned it from new since roughly 2001/2002ish. Gigged a handful of times, but basically a bedroom amp.
I was playing through my Digitech RP-14D into the clean channel, with the volume on the amp turned up to somewhere around the 10 or 11 o'clock mark, so not pushing it at all!
after abt 10-15mins of playing the volume coming from the amp noticeably dropped, as did the clarity of the sound. It sounded almost like someone had walked past and knocked both the volume knob, and the tone knob on my guitar.
i continued to play, and the sound would change back and forth from how it should be, to the quieter muffled sound every 2 or 3 mins or so.
i have noticed the amp do this once before (i havent played much recently), and that time i was just plugged straight into the amp, using the clean and OD1+2 channels, and it was the same.
this leads me to believe that either its the amp or the guitar itself, so the Digitech pedal can be ruled out.
the amp only has 1xECC83 (12AX7) pre amp valve in it, which ive changed twice over the life of the amp so far. but ive never experienced this problem before.
anyone got any ideas as to what it could be or where to begin with diagnosis?