A self built JTM45 is the most flexible amp???

Discussion in 'Amps and Cabs' started by MK50H, Jun 13, 2008.

  1. MK50H

    MK50H Member

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    I have been kicking around some ideas for a new amp for ages, and I have (I think) decided that a self built JTM45 is the most flexible amp (for me at least).

    I want to lay out my thinking for others to comment on, just to see if my plans "hold water".

    So, I really want just one amp to cover everything from Indie Pop, through to Metallica. My main tone is something from lightly warmed up clean to overdriven blues/rock tones. I think that Paul Kossoff (Free) sounds on the Fire & Water album are probably what I am shooting for although I haven't listen to that album for ages...

    Therefore, I am thinking that I should aim for something that does a good clean, and leans nicely to the Blues/Rock thing. The JTM45 seems perfect for this.

    The other thing that I really like about the 45 is that it is a very widely understood & discussed circuit. I feel that I should be able to tweak/modify anything to perfect the tone. Of course, it ain't a JCM800 but I think I can get a usable imitation with a good pedal & switchable SS rectifier. I am intending to build a couple of cabs with different drivers so that should get me more tonally variety too.

    What do you think, does this make sense?
     
  2. Flux

    Flux Member

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  3. hamfist

    hamfist Member

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    Similar to Flux's response, maybe an earlier 1987-type circuit, with EL34's, SS rectifier, but with the earlier shared cathode pre-amp configuration might be a bit more flexible, and help everything keep rather tighter when you are pushing it with a pedal.
    I just don't think KT66's will cut it in any way with Metallica-type tones.

    Oh, don't forget that Lar-Mar PPIMV !! As you'll be wanting to keep your hearing intact no doubt !
     
  4. MK50H

    MK50H Member

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    Thanks guys, I appreciate your comments,

    I was probably exaggerating a little with the need for Metallica, but I want to get somewhere near that territory on occasions. So I hope you get the idea.

    Anyway, I really want KT66's, for their softer tone. but I also feel that maybe they are too soft for more aggressive tones.

    So, I dunno. Maybe I should build two amps, one in the KT66 JTM45 zone, and a more aggressive EL84, SS rectified one. If so what models with you use as the starting point? JTM45 & 1987X?
     
  5. dk123123dk

    dk123123dk Member

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    Didn't Paul Kossoff use a SuperBass?

    dk
     
  6. MK50H

    MK50H Member

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    Dunno, I've read that he used JTM45, some kind of Orange, and Fender amps (in the studio I think). I'm guessing he used JTM45/100 and probably a lot more besides.
     
  7. hamfist

    hamfist Member

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    The Jtm45 and the 1987 sound like great starting points to me.

    (yes, I know you mean EL34's)
     
  8. MK50H

    MK50H Member

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    Doh, I hate it when that happens :eek:
     
  9. Flux

    Flux Member

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    You can still use the JTM45 architecture with it's GZ34 rectifier by substituting the tube with a socket mounted SS rectifier - like the Weber Copper Cap. You can also swap 6L6, KT66, or EL34's. However, to do this you must first make sure your power transformer is up to the task and remember to jumper Pins 1 and 8 on the power tube sockets (+ don't forget to re-bias after changing tubes). The Yahoo JTM45 user group should have this and other info.

    The JTM45 was the first Marshall and can be morphed into later versions, which is another reason why it's a popular choice. As a final note let me say that if you do choose to go this route, pay real close attention to your choice of output transformer. Depending on where you want to end up, it can make a huge difference (i.e. research the OT primary impedances and the prefered reflected plate impedances of the power tubes you want to use)
    and opinions do vary somewhat... Once again, lots of info available.
     
  10. MK50H

    MK50H Member

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    Thanks guys, really useful info.
     
  11. 908SSP

    908SSP Supporting Member

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    Metallica used 6L6 tubes in the their Boogies a lot closer to KT66 than EL34s. But I don't think a JTM45 is the way to go. It won't cut it from the get go so you're modifying it right off the bat when there are better starting points. A 1986 Plexi is the bass model 50 watt with EL34s and SS rectifier has much better bass so you can feed it a metal style pedal and it wont flub out like a JTM45. But there are lots of other options out there. SLO 50 clones you could build with channel switching 6L6 or KT66 tubes and high gain all for the same out lay as a JTM45 just a bit more work.
     
  12. JimmyR

    JimmyR Member

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    I prefer the 1987 to the JTM45. Although they ARE very similar there is quite a difference in tone. I would strongly recommend checking out Metroamp.com. I have built more than a few amps with parts from there and been extremely happy with them. For Free type tones the 1987 works better than a 45. I like to use .1uF output coupling caps in the 1987 though for a bit more low end with a 2x12 open-backed cab.

    If you build a 1987 style amp there are lots of mods you can try, and it's easy to try KT66s in it with a simple rebias. My last 1987 was a '68 spec with split cathodes on V1 and it sounds incredible with all my guitars - a very versatile amp.

    You might also want to check out the new Roccaforte kit that Mojotone is producing - sounds like it could be right up your alley.
     
  13. ROKY

    ROKY Member

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    I would go with the 1986 model, also, with a higher value bright cap on
    one of the channel volumes .

    You could run a nice pair of EL34s or KT88s if you wanted the Park 75 vibe
     

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