Marshall JMP '78 circuit help please!

Discussion in 'Amps and Cabs' started by jonassweden1, Apr 17, 2016.

  1. jonassweden1

    jonassweden1 Member

    Messages:
    23
    Joined:
    Jan 18, 2011
    Location:
    Stockholm, Sweden
    [​IMG] [​IMG] hello guys!

    Please find pics of my 2104 circuit board. I now there are some non stock components and also push pull pots installed on the volume/pre knobs.

    But - interested in the tone stack components. The tone is a bit hard, attack to fast. I miss some 'sag' for better words. Specifically talking about the disc above 'Marshall' and the red bean above 'ST1'.

    They came back after visit at tech changed vs. what was in there before. What values should they have stock??

    Anything else notable?

    Cheers
    Jonas

    [​IMG]
     
  2. DrainBamage

    DrainBamage Member

    Messages:
    2,327
    Joined:
    Sep 23, 2011
    Well I might not have to best answers for you. But it appears all coupling caps (round yellow caps) have been replaced. The yellow circle should be a 470p/500p ceramic disk and it goes in the open slot on the board next to it but does the same thing how its now. The red caps on the jack and board look suspicious. The red arrow with the caps after the 10k isnt right. The 100k in the PI. I cant really see the whole board clearly. This is based off of my knowledge of pictures of late models JMP.
     
  3. GilmourD

    GilmourD Member

    Messages:
    1,323
    Joined:
    Jun 8, 2006
    Location:
    Rutherford, NJ
    Dunno if this helps, but it's a pic of a 2204 board. The 2104 was just the combo of the 2204.

    [​IMG]
     
  4. walterw

    walterw Gold Supporting Member

    Messages:
    34,245
    Joined:
    Oct 16, 2006
    you can't just mention push-pulls on an old marshall and not tell us what they do! :waiting
     

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