JCM900 problem - advice needed

tony77

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Apr 16, 2019
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Hello everyone,

[FONT=&quot]I 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.[/FONT]

[FONT=&quot]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?

Thank you![/FONT]
 
I'm assuming you tried a replacement 12ax7 and swapped in with each of the pre-amp tubes?
What you describe has usually been preamp tubes in the handful of times it's happened to me with my amps.
 
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