'80 JMP 2203 stock components?

Discussion in 'Marshall Amps' started by jhullin, Feb 27, 2020.

  1. jhullin

    jhullin New Member

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    Hello, was looking for some help on my amp. Mainly the small ceramic caps at V1 socket and the cap across the plate resistor. I have already put a 10k piher back in V1B cathode, removed the added cap across V1A cathode so........... were the other caps added to tame these mods? Would the amp had come from the factory with both the hot shield and a cap across plate and grid of V1A? Appreciate any help..............
    [​IMG]
     
  2. ampmadscientist

    ampmadscientist Well-Known Member

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    This is negative feedback to kill the hiss ringing microphonics etc.
    The hot shield is a factory installed item, and so is a NFB cap between pin 6 and 7.
    Somebody has changed the cathode resistor of V1A (call it V1B if you like) to 3K ohm. Normally this resistor would be 10K I think.
    Somebody has added a bypass cap across V1B (call it V1A if you like) cathode resistor (to increase lows and some gain added)
    There is a bypass cap across V1B (V1A) plate resistor to limit high frequencies, that is also done to decrease hiss.

    Well, they increased the gain and decreased the hiss / highs to get rid of the added noise.

    Do you want to put it back to stock?

    I have never seen the factory install hot shield and feedback cap pin 6 to 7, both at the same time.
    They usually just do one not both.
    I personally suspect that this cap pin 6 to 7 may have been added but I may be wrong and there's a first time for everything.

    That cap pin 6 to 7 looks like a stock cap that's the only thing it doesn't fit.
     
    Last edited: Feb 27, 2020
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  3. jhullin

    jhullin New Member

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    Thanks for the reply.... Yes, I think I'd like to put it back to stock. I've already changed the 3k resistor back to 10k and removed the added bypass cap on the V1b cathode resistor. Love the amp but wondering if I should remove the rest of the non-stock caps.
     
  4. GIBSON67

    GIBSON67 Well-Known Member

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    Here's my old 1980 2203 that was pretty close to stock.

    Input 2.jpg
     
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  5. jhullin

    jhullin New Member

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    @GIBSON67 Thanks for the pic!! That helps alot
     
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  6. ampmadscientist

    ampmadscientist Well-Known Member

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    A. The bypass cap across the V1B plate resistor. This kills the highs but also kills hiss.
    B. The bypass cap across pin 6 and 7. This is doubling the hot shield basically and trying to kill hiss and highs again.

    So it's either the hot shield -or- the bypass cap pin 6 and 7 has to go...
    There will be increased hiss but the highs will come back.
     
  7. GIBSON67

    GIBSON67 Well-Known Member

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    Great amps, BTW...I've had two JMP 2203's and they were both my favorite amps of all time!
     
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  8. ampmadscientist

    ampmadscientist Well-Known Member

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    Thanks for the picture nice one.
     
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  9. jhullin

    jhullin New Member

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    Is it safe to say the bypass cap across the V1B plate resistor was needed for the mods I've already removed? Not needed anymore? I'll remove the caps on the tube socket but the one on the board wont be as easy to just lift a leg to see how it sounds
     
  10. jhullin

    jhullin New Member

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    Totally agree!! Love this amp
     
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  11. ampmadscientist

    ampmadscientist Well-Known Member

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    Take out the cap between pin 2 and 3 of the first preamp tube (also) besides...
     
  12. ampmadscientist

    ampmadscientist Well-Known Member

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    Yes
     
  13. ampmadscientist

    ampmadscientist Well-Known Member

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    you can just cut the one on the board
     
  14. jhullin

    jhullin New Member

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    @ampmadscientist Thanks a TON for your help. Really appreciate it................
     
  15. ampmadscientist

    ampmadscientist Well-Known Member

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    I can't wait to hear it....:lol:
     
  16. jhullin

    jhullin New Member

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    Well.........could you hear it? :) It'll definitely peel the paint off the walls. Did a quick snippety snip on the caps. The amp was great but even better now!! Thanks again for the quick help..............
     
  17. ampmadscientist

    ampmadscientist Well-Known Member

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    Turn it up more.:agreed:
     
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