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JCM900 - urgent advice needed

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  • JCM900 - urgent advice needed

    Hi all, Ive got a 4500 model (head) I'm getting intermittent volume drops and can't figure out what's happening...

    This model has a separate master volume for each channel but its happening on both which says to me it could be the power amp stage...

    had a look at the valves (marshall branded EL34's for those who care) they're all glowing happily, Ive run it at 25 watts and tried 1 valve at a time,
    tried with different leads, tried cleaning the pots and checked the entire thing for dodgy soldering/connections, tried wiggling leads at i/p n o/p, different cabs etc

    I'm stumped and have an v important gig in about 21 hours or so and my only backups are a pod xt live through the PA or my mate's valvestate - nuff said eh?

    On the plus side though its not half as bad once she's warmed up a bit but I can't gig it in that state - any advice/diagnosis???

  • #2
    Do you have an effects loop? Try jumping that with a cable and see if that clears it up. If so, those jacks could need some cleaning.

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    • #3
      Originally posted by Garydean View Post
      Do you have an effects loop? Try jumping that with a cable and see if that clears it up. If so, those jacks could need some cleaning.
      What he said......
      The farmer takes a wife, the barber takes a pole....

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      • #4
        Genius! cheers Theres a load of gunk on the send socket, bridging seems to help so I'll pick a new 1 up tomorrow

        1 more prob though... theres a fx level dial which peaks halfway in between high and low then drop either side... don't suppose ya know if thats normal or whats causing it?

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