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Marsahll (Stewmac) Clone Bus bar grounding scheme

Discussion in 'The Workbench' started by heave1, Sep 28, 2021.

  1. heave1

    heave1 New Member

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    Is there a bus bar grounding scheme for a JTM62 Plexi 45 Watt amp similar to Rob Robinette's bus bar grounding on Fender amps?
     
    Last edited: Sep 28, 2021
  2. heave1

    heave1 New Member

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    It's for a Stewmac 62 Plexi 45 Watt amp kit.
     
  3. XTRXTR

    XTRXTR Well-Known Member

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    If it has 3 12ax7s and 2 power tubes you should be able to follow the one he has for the bassman or the 2104 below, I'm doing a 2204 rebuild and follow the 2104 scheme. I think the bassman is better for your amp.

    The entire preamp bus is grounded to chassis at one point - the guitar amp input jack or very near with a separate bolt. Note the B+3 and B+4 caps ground to the preamp ground bus, The bias filter caps and bias resistor are grounded to the preamp bus, the V1 and V2 cathodes are grounded to the preamp bus, the Volume pots and the Mid pot are grounded to the preamp bus. The Presence ground is shared with the PI tail and the NFB resistor and separate from all other grounds (he suggests a very tight star washer to ground it to chassis) B+1, B+2 caps are grounded to a chassis bolt on or near the Mains transformer, with the Heater CT. HV CT gets soldered to the neg terminal of the Resevoir B+1 cap. Mains earth safety gets its own bolt not shared.
    https://robrobinette.com/images/Guitar/Bassman/5F6A_Bassman_Amp_Layout.png
    https://robrobinette.com/images/Guitar/Marshall/JCM800_Overdrive_and_Tone_Tweaks.pdf
     
    Last edited: Sep 29, 2021

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