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Help biasing marshall DSL50

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Roodboy, May 15, 2011.

  1. Roodboy

    Roodboy Member

    Messages:
    1,471
    Joined:
    Jun 1, 2004
    Location:
    Long Island
    I am trying to bias a dsl 50 head and can't locate CON2 or minpots PR1 or PR2 as mentioned in the link to instructions and schematic
    http://www.drtube.com/schematics/marshall/JCM2000%20Bias%20Instructions.gif
    http://www.drtube.com/schematics/marshall/jcm2-64-02.pdf

    Here are pics to the amp:
    [​IMG]
    [​IMG]

    [​IMG]

    Can anyone pont out where CON2 and the bias pots are?
    I see three different CON2 one on each board but none look to be connected to a CON1 with 7 wires like the schmatic shows and I have no idea where the mini pots are.
    Thanks
     
  2. WaltC

    WaltC Member

    Messages:
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    Feb 21, 2006
    Location:
    Northern CA (Sacramento area)
    it's not necessary to take the chassis out of the box to do this. The board you're looking for is accessible from the outside w/ the metal back panel off. It has some pins and two small plastic pots showing in a cutout on the top edge of the chassis between the power tubes. You put a Multi-meter (set to dc volts) neg lead on the middle pin and the positive lead on either the left pin or the right pin and adjust the pot next to the pin to the appropriate setting pointed out in the first Marshall tech note you have listed above.

    *Any* reputable amp tech in your area that works on Marshalls has done this dozens of times and could (if he wished) show you how to do it. You might offer to compensate him for his time, that'd be neighborly.
     
  3. Roodboy

    Roodboy Member

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    Location:
    Long Island
    Thanks
     
  4. mojoalb1

    mojoalb1 Member

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    Jul 27, 2010
    There's a good video how to at eurotubes.com. Shows exactly how to bias a dsl amp. he shows on a 100 and says it's the same fore a 50 just half the power.
     
  5. Roodboy

    Roodboy Member

    Messages:
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    Location:
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    Thanks, heres the link for anyone that stumbles into this thread in the future
    http://eurotubes.com/euro-Marshall-DSLTSLV.htm
     
  6. renato-rt

    renato-rt Member

    Messages:
    358
    Joined:
    Oct 11, 2011
    Location:
    Music Land
    I want to replace the power tubes of my DSL50 and then adjust the bias. Neither this Eurotube guide:

    http://eurotubes.com/euro-Marshall-DSLTSLV.htm

    and this Mtroniks guide

    http://www.youtube.com/watch?v=1CSZEjoWjgs&feature=fvsr

    mention the need to measure the plate voltage.

    They both tell to stick with the stock standard values. In the case of the DSL 50 it is something between 40 and 45 mV.

    I'm really in doubt, because I have seen a lot of people talking about the need to measure the plate voltage for the DSL, like in this guide here:

    http://www.lydian.ca/Marshall_DSL_Bias.html


    What to do?
     

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