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  • #1

    Jcm 900?

    Hey guys, I have a JCM 900 and I'm wanting to convert it over to a JTM 45 plexi. Would this be possible? I was thinking od getting a JTM 45 faceplate and backplate and convert it over using the samre chassis and tranny's etc. If the chassis and tranny's are usiable for the conversion I was thinking of using a tag board for ptp wiring instead of the circuit board that's in it now.Or can I use everything that's in the amp as it stands now with only a few mads? I've never tackled a Marshall project before so I'm woundering if I'm getting in over my head with this? I have built a 59 Bassman,57tweed deluxs ,Bad Cat hot Cat 30,& 15, AMatchless Lightning,etc.I built all these amps with alot of help from you guys here on the fourm. Am I being to ambitous?

    Chuck.
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  • #2
    Anyone with suggestions on how to approach ?

    chuck.

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    • #3
      There are several models in the JCM900 series. Some have lots of solid state circuitry. What model is yours? It would be a model number like 2500, 4500, 4101, something like that. Is it one of the amps with the gain that goes to 20?
      WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
      REMEMBER: Everybody knows that smokin' ain't allowed in school !

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      • #4
        I looked in the back of a JCM900 series amp at a guitar show yesterday and the tubes were in a line just behind the front panel controls, not in the back like most prior Marshalls. That might make for a very unusual layout. Please provide pics of your amp.
        WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
        REMEMBER: Everybody knows that smokin' ain't allowed in school !

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        • #5
          If you've built a bassman, you've pretty much built a JTM45
          The JCM900 will be a larger chassis than a JTM so you should have plenty of space to accomodate a layout.
          You will need to punch/cut a hole for the tube rectifier, and some front panel holes will not be used.
          The JCM PCB's are pretty horrid to work on, tracks lift etc, I wouldn't recommend modding the PCB, therefore a tag board/turret approach is good

          There is plenty of internet support/layouts for JTM's so you should have no problems there.

          My only concern is the iron used in the JCM900, the trannys are pretty weak IMO.
          I have a 66JTM and had a 100WJCM900 for a while and the JTM blew it away for clarity power and volume.

          If the intent is to get a faithful reproduction of a JTM, I would suggest the trannys are not going to give that too you.
          But otherwise it should be a fun project.

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          • #6
            Some reports about simply removing the diode clippers from the 900 series are very positive. As noted, if you've built a 5f6a you've built a jtm45.
            "Take two placebos, works twice as well." Enzo

            "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

            "If you're not interested in opinions and the experience of others, why even start a thread?
            You can't just expect consent." Helmholtz

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