Hi, was wondering if someone could give some insight into a problem with my Marshall JCM900 combo.
I was about to soundcheck the amp at a gig recently, clicked on a few pedals for checking the loud sound and the amp's volume suddenly dropped significantly. I could turn it up to a barely manageable stage volume at around the 8 mark, but there was still a slight horrible top end crackle, like a busted speaker or something.
I tried changing the power tubes but it made no difference. Any amp techs out there got any vague ideas of what might be the problem?