Jmp /jcm 800

Discussion in 'Marshall Amps' started by RLC, Apr 4, 2021.

  1. RLC

    RLC New Member

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    I reckon I should sell my JCM and keep my jmp then. Any offers?
     
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  2. Brett336

    Brett336 Member

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    I have an '82 and an '83 JCM800 2204. The plate voltages are 410V and 490V respectively and I do personally plate the '82 (410V) more often due to the sweater, smoother distortion.

    They are both 4010 combos and schematically are different from my 2203 head in that the combos had a capacitor across the mid tone pot to give is a little different midrange to compensate for the open back combo cab. They are all great depending on your mode. I don't buy into one is better than the other. It's really personal preference. And if you have never have all of the examples to try, you really don't know any better - just play your guitar...
     
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  3. AndyD

    AndyD Well-Known Member

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    Hi, I think Kelia above offers one of the significant differences. The vertical input JCMs were essentially the very last of the JMPs and yes, they are much easier to work on and are less likely to give problems with fatigued connections between the pots and circuit board. I have three JMPs and in the past owned a late 80s JCM and I would agree that the JMPs have a “sweeter” tone.
     
  4. dslman

    dslman Well-Known Member

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    Any exp. with the Ceriatone vertical inputs 2203/4 compared to your JMP's?
     
  5. AndyD

    AndyD Well-Known Member

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    Hi, sorry no I haven't. So much depends on the transformers used, B+ voltages and make of components.
     
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  6. dslman

    dslman Well-Known Member

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    True, it's been so long since I had my old 1980 JMP 2203, but my friend built me a Ceriatone 2204, and the plate voltage is 430v on this one. It's a fantastic amp, and really reminds me of my old JMP.
     
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  7. AndyD

    AndyD Well-Known Member

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    I think 430v on the plates is a great value. I think it tightens up the sound perfectly without getting too stiff. I have a '79 2204 with a replacement power transformer that gives 450v on the plates and its a fantastic amp.
     
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  8. dslman

    dslman Well-Known Member

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    I think so too, I was happy when he told me it was 430. I bet your 79/2204 is a wonderful amp for sure.
     
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  9. LargeBoxSmallBox

    LargeBoxSmallBox Well-Known Member

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    my '77 2204 has a full compliment of mustard caps from the factory, and it does make a difference. The subsequent green cap JMP 2204's and white cap JMP 2204's both sound amazing, and a little but not that different, IMO. The red cap amps that started being produced in 1980 were not as good sounding, IMO, though still really good. Right after that came the JCM 800 series, still with the red caps. Yes they still sound good, but it's different forever after those red caps started being used.

    I love the mustard caps, myself, all my favorite old amps are from the mustard cap era. There's a reason you see those old amps so often with all the mustards robbed! Those caps are only one aspect of the amps, but they do make a difference, to my ears.
     
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  10. dslman

    dslman Well-Known Member

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    I wish I knew for sure what year my old 2203 was, either late 70's or 80, it had the rocker switches and the JMP headshell with the large logo, and vertical inputs.
     
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  11. LargeBoxSmallBox

    LargeBoxSmallBox Well-Known Member

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    450V on a 2204 is a high voltage amp, and should sound REALLY good. In my view, a lot of the really great old Marshalls had high voltage. My Plexi has over 500V, and it is an amazing sounding amp. There is such a thing as too much voltage, but a 100-watt Marshall with 500-530V will usually be an amazing amp (all other things being right), and will tear your head off (in a good way!).
     
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  12. LargeBoxSmallBox

    LargeBoxSmallBox Well-Known Member

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    490V is very high for a 50-watt amp! After the early 70's, most 100-watt amps in the USA market were less than that. You could still get higher voltages in Canadian amps for awhile, but 490 in a 50-watt amp is a lot of voltage.
     
  13. Kelia

    Kelia Well-Known Member

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    If your old 2203 sounded like this one , hope you're still kicking yourself
    for letting it go ,..Lol :D

     
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  14. Brett336

    Brett336 Member

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    Yeah, I was surprised to see that much voltage and checked my multimeter to see if it was reading correctly. I was also surprised to see that my '82 was slightly over 400 volts since I expected the late JMP to come in around 375 volts.

    It probably for this reason and hundreds of other component variations that all Marshalls need to be judged with your ears and fingers - even between two of the same model and year.
     
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  15. dslman

    dslman Well-Known Member

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    I would have never sold it, but sadly it was stolen from our band room.
    That’s a nice specimen for sure.
     
  16. Maggot Brain

    Maggot Brain Well-Known Member

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    I once owned a '83 2204 vertical input and then later a '87 or '88 horizontal input. I foolishly sold my '83 2204 which was the most incredible amp I'd ever played... years later I came across the horizontal input hoping to recapture the magic of the first amp... The horizontal input while a good amp and a Marshall no less it just didn't have the mojo of the vertical input... Now I suspect that it may be related to tubes more than anything else. Weren't the earlier 2204s running 6550s? I believed it had Westinghouse preamp tubes. I believe the horizontal 2204 had EL34s and I am unsure what preamp tubes it had... I could be wrong.

    Anyways that '83 JCM800 2204 was the pinicle of tone... kick myself nearly every day for selling it.
     
  17. dslman

    dslman Well-Known Member

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    I was under the impression that a bit lower plate voltage would get you a bit more sag, and into the VH tone a little easier.Maybe not as tight as the higher voltage amps.
     
  18. AndyD

    AndyD Well-Known Member

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    True indeed. The plate voltage offers different experiences. No right or wrong.
     
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  19. Kelia

    Kelia Well-Known Member

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    Oh wow ! That sucks big time ! :mad:
     
  20. dslman

    dslman Well-Known Member

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    This is true my friend. Still hurts after all these years.
     
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