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Strange Marshall 1987x issue

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by jezzzz2003, Jun 4, 2006.

  1. jezzzz2003

    jezzzz2003 Member

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    aussie
    Hi there,

    I have never had a problem with my reissue Marshall in over 1 year of gigging with it but about a week ago I was trying out a new overdrive pedal when all of a sudden I heard a drop in volume followed by a burning smell.
    I quickly looked through the back grille and saw a tube really glowing colpletely orange.
    Switched it off immediately and had it checked with my tech.
    He found nothing and since then I have gigged with it twice without a hitch, tubes were replaced with Svetlana winged C two months ago.
    Does anyone know what may have caused this?
    Its these little things that keep you up at night...:cool:
    Thanks guys.
     
  2. gtrnstuff

    gtrnstuff Member

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    Middle TN
    So the orange tube lived? Usually a red plate means a bias problem, but if your tech checked it out and found no cold solder joints or other intermittent stuff...enjoy it until it wacks out again. Carry a spare, if you can.
     
  3. donnyjaguar

    donnyjaguar Member

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    The Marshall's that I've seen have the bias circuit cleverly designed in such a manner that its not very likely the amplifier will lose bias. If it did I do believe both, or all four if so equipped, tubes would be glowing red. Catastrophic failures of power tubes seem to be higher in true power-pentodes (EL34) and my guess is that the one tube went bad. Throw it over your shoulder and get on with life.

    DJ
     
  4. jezzzz2003

    jezzzz2003 Member

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    You guys are legends!
    Thanks for your help.
     
  5. sinner

    sinner Member

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    I had a similiar problem with my 1987XL, playing pretty low and with a PowerBrake and lots of gain from pedals--and the sound suddenly got garbled, then the smoke came out from the back grill heading to the ceiling. I shut down and took it in. One bad power tube, no other damage--even checked the PowerBrake. Funny, the tubes were pretty new, not many hours of use, but since the change (and biasing) not had any other issues--and still using lots of pedals.
     

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