saviogomes

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?

When i play, ill set everything as i want, whether that be with presets or an original tone. Speed Test Scrabble Word Finder Solitaire I start playing then all of a sudden it just goes really faint and no matter what you do you cant turn it up. then after about 5 mins it spikes (if the volume knobs are turnes up) so i turn it down but as soon as you touch the volume it just goes really faint and stays there???? and the tuner doesnt work =( plz halp