50 watt 1978 JMP modded to plexi?

Discussion in 'Amps and Cabs' started by Hand of Doom, Oct 17, 2005.

  1. Hand of Doom

    Hand of Doom Member

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    Can it be done and is it costly to do? Who would you recommend to do the job? I am in the Houston area but would by more than happy to ship the amp anywhere in the USA. I am not worried about degrading the value, I will not sell.

    I am basically looking to turn it into a very aggressive dynamic amp without a gain knob. Like EVH on VH2.
     
  2. Swarty

    Swarty Member

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    It can be done, however the voltage is probably going to be a bit on the low side. You can always have a hotter power transformer put in. Basically get a schematic for the plexi circuit you want (there are a bunch) and take it to a guy in Houston who knows guitar amps. It is not a big deal at all. Change a few small parts and some filters and you're there. I doubt, however that the resulting amp will be any more aggresive than the one you have... but it will be darker and smoother.
     
  3. Hand of Doom

    Hand of Doom Member

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    sounds good…that’s what I want….dynamic without that Gain knob harsh drive.
     
  4. Ship it to VoodooAmps.com

    Imho an EVH style sound in your 50 Watt would require an OT and choke swap and some (small) tweaks, if it's still too loud ask for a GOOD MasterVolume-control.

    Hope this helps,
     
  5. Hand of Doom

    Hand of Doom Member

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    VoodooAmps? I will check 'em out, thanks.
     
  6. Roccaforte Amps

    Roccaforte Amps Member

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    Its the output transformer that will need to be changed,
    and some other parts.
     
  7. Hand of Doom

    Hand of Doom Member

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    thank you for your replies
     
  8. Swarty

    Swarty Member

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    I think it would be at least equally important to get the voltage up where it should be. A 50w '78 is typically under 400V.
     
  9. Roccaforte Amps

    Roccaforte Amps Member

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    So are most 50watt Plexis.
     
  10. Hand of Doom

    Hand of Doom Member

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    this is getting good, thanks. Will these changes increase the over all vol.?
     
  11. Swarty

    Swarty Member

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    A 50w plexi is typicall around 440v wheras a '78 is typically around 380V.
     
  12. Roccaforte Amps

    Roccaforte Amps Member

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    Not all, most are lower.
     
  13. JWR

    JWR Member

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    Why hack a perfectly good JMP? I just don't understand why you wouldn't just get the amp you need. Sorry, just my personal opinion.
     
  14. Hand of Doom

    Hand of Doom Member

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    good question and I agree with you 100%

    I bought the amp for a good price a bout two years ago. back then I didn't know what I wanted as far as tone. I had always been a Fender guy.

    After buying a Germino Classic 45, I know I like non master volume amps.

    After doing some research on the tone I want, I came to the conclusion that I would probably save money modding the JMP. I like what it does and it does it well but it is just not me.


    P.S. Being a total n00b I had the amp sent to a friend to take the master vol. out....like what I have heard done to Fender master vol. amps. Boy was that a mistake. I did the total opposite to what I actually wanted.

    live and learn....er...ask people who know...like at this great place.

    Thanks for all the input.

    :)
     

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