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musicmaster circuit help?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by smolder, Feb 14, 2009.

  1. smolder

    smolder Gold Supporting Member Silver Supporting Member

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    Anyone have a pic of an original musicmaster circuit/chassis? I just picked one up and it looks funky... trying to decide just how original it is.

    Also... has a G12M 70 that appears to have been made in England... sure they are not uncommon, but I have never seen or heard anything about them. Any one got an impression?
     
    Last edited: Feb 14, 2009
  2. smolder

    smolder Gold Supporting Member Silver Supporting Member

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    ok... maybe I am approaching this wrong...

    does this circuit look like it has been altered or had the caps replaced? Its a 1978.

    [​IMG]

    [​IMG]
     
  3. Ronsonic

    Ronsonic Member

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    The Illinois caps are definitely not original.

    What is wrapped around the one on the end? If that's a clamp holding it to that screw on the end of the board, okay.
     
  4. smolder

    smolder Gold Supporting Member Silver Supporting Member

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    It is a clamp. So I guess the filter caps are new... the way that one on the end is wired and soldered seemed very non fender and non factory, but its a 78... a little later than I am familiar with.

    The red plastic wire (most is cloth here) coming from the audio transformer (is that a choke?) has a burn mark... so I knew something had been done.

    I found schematic... so I can step through that and compare, but any other observations would be helpful. This is an odd amp and there is not much online about mods... looks kind of like a champ with 2 power tubes.
     
  5. Cornbread

    Cornbread Silver Supporting Member

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    Hey Smolder, I have one of those myself (since Jan '05) and play it every single day. I really love it.

    There's a lot of information over on tdpri.com Rob DiStefano (who posts at tgp and tdpri) knows a bunch about them.
     
  6. smolder

    smolder Gold Supporting Member Silver Supporting Member

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    Thanks Cornbread... I checked out all of the threads. It looks like the common take is to upgrade the speaker and otherwise leave it be.

    I was looking for a 10-12 watt... something SF but just a bit bigger than my champ. Not quite ready to bite the bullet on a princeton reverb. For the money this thing is great.

    I put some JAN Sylvania 6V6's and a GE 12AX7, along with a Greenback. It really sings. I also tried a V30... but I like the scooped mids a bit better.
     
  7. Ronsonic

    Ronsonic Member

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    I modded one of these with a preamp section from the tweed Vibrolux. Very, very sweet. The thing would do feedback at living-room volume. Yeah.
     
  8. BluesForDan

    BluesForDan Member

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    Could you tell me more about that preamp section?
     
  9. hasserl

    hasserl Member

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    Take a look at the Vol/Tone circuit from the tweed Harvard 5F10. IMO this is a much preferred circuit over the stock MMB Vol/Tone circuit. Just rewire it as so and enjoy. SOme folks like to remove the .0047uf cap on the input and replace the 470k grid load resistor w/ 1M so it doesn't load the pickups down as much. I've not done this mod and am happy with mine with 5F10 Vol/Tone circuit. BTW, I'm running a Weber Alnico Signature 12 and that's a good match for this amp.
     
  10. Ronsonic

    Ronsonic Member

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    Basically I just grabbed the map for the Vibrolux (probably no different from the Harvard hasserl was talking about) and changed everything before the driver tube to match. Much livelier and gainier circuit than the MMB preamp. That was a few years ago and I didn't really make any notes or anything, just soldered and bodged it together.

    Not exactly a high gain amp by any measure but sweet and nasty. I went with the Tweed Vibrolux circuit because I had one of those amps and liked it.
     

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