Issue with identifying proper schematic

Discussion in 'The Workbench' started by justsomeguy, Jan 16, 2021.

  1. justsomeguy

    justsomeguy New Member

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    I have some work to do with my 50W JCM900 SL-X, built in 1993.

    Inside the amp it has the SLXa-66-00 board (issue 3-45), but every website I've checked (tube store, dr tube, etc) shows the following when I select my amp:

    SLXa-61-02
    2500-60-34
    2500-60-02
    2500-60-58

    Am I missing something?
     
  2. South Park

    South Park Well-Known Member

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    Are the replacement boards made by Marshall same part number . Do those boards have a schematic with them
     
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  3. mickeydg5

    mickeydg5 Well-Known Member

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    Their schematic numbers do not really or totally match up with board numbers.
    In fact most of their crap has little rhyme or reason.
    Do not worry about it.
     
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  4. Gunner64

    Gunner64 Emotional Support Animal Gold Supporting Member

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    5881's or El34's? Use the schematic for your amp. Dr. Tube has them.. And use the Early preamp schematic. Don't go by the board number in your amp.. I agree. Some Marshall schematics are hard to decipher..the sl-x is one of them.
     
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  5. justsomeguy

    justsomeguy New Member

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    Roger. Will trust the websites built by people with decades of experience then, just seemed odd.
     
  6. justsomeguy

    justsomeguy New Member

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    EL34. The Dr Tube ones I've been looking over and comparing to my board and while the schematic designator isn't the same, it appears the circuit is. Thanks.
     
  7. Gene Ballzz

    Gene Ballzz Well-Known Member

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    A hearty :welcome: to the forum!
    That's All,
    Gene
     
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  8. mickeydg5

    mickeydg5 Well-Known Member

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    In different words do not trust anything about Marshall. When it comes to documentation and standards they are a bunch of dingleberries.

    Sometimes component numbers are changed and sometimes even components values change per revision. So there are variations with any one amplifier model as well as all.
    But usually the majority or core design and layout remain the same.
     
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  9. cruisemates

    cruisemates Active Member

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    I almost hate to admit this, but I was given a chance to write an amateur-tech article for a major web site, but they gave me the topic "History of Marshall, the Early Days." When I started doing research (going by memory here) there really was no rhyme or reason. The company just changed things all the time - there was hardly any specific topology, especially to the early models. In fact, they made a 100-watt lead (+ a 200-watt called the Beast), the 50-watters, etc. They gave them model numbers that looked like years in the future (the 1987, etc).

    The Plexi and Super-leads (really the same thing IIRC) were the first production line models that they did mostly the same. There were a few one-offs before that. Then came the 2203, 2204, and those stayed the same for far longer than most people probably think.

    Weirdest of all - they made amps that were anywhere from 1 to 8 pre-amp channels - but they are all the same component designs, just different numbers of pre-amps. The (earliest) bass amps were no different from the guitar amps AND they even made an 8-channel "PA Amp" that was just 8 of the same guitar preamps. I don't even think it was low impedance.

    I REALLY tried to stay away from too many tech details, like when they started LTP rects, because there was always someone who had an exception to any information I found. Of course, when the article came out there were a bunch of know-it-alls who criticized its accuracy, but the website had actually given the first draft to Marshall to verify it, and it took Marshall months to get their own version back to the website. Even Marshall didn't know what was up.
     
  10. mickeydg5

    mickeydg5 Well-Known Member

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    Yes agreed. I have been looking at Marshall stuff for a long time.

    However, do tell me what a LTP rect may be?
     
  11. cruisemates

    cruisemates Active Member

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    Long Tail Pair - sorry
     

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