Vintage Inspired Jtm45/100 Block-end Build

Discussion in 'Building the Classics' started by valvestorm, Dec 23, 2016.

  1. soundboy57

    soundboy57 Well-Known Member

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    Just a stunning piece of work. Wow, nice job :)
     
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  2. Notthedocter

    Notthedocter Member

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    Very nice build! thanks for sharing the pics...
     
  3. valvestorm

    valvestorm New Member

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    Thanks Guys! Sorry to resurrect an old thread! I finally got around to build another one of these. The new one is running a bot lower (490v) on the plates than the original (495v). Carl and Neil were having a discussion earlier about tweaking the 8.2k decoupler to adjust the down stream voltage. Unfortunately the original amp had already shipped, so I did not get a chance to tweak those voltages. What voltages do you guys like for the v3, v2, v1 anodes for these?
     
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  4. ibmorjamn

    ibmorjamn Well-Known Member

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    I have never seen the block ends , did Marshall use those in the early builds ?
    Nice build !
     
  5. valvestorm

    valvestorm New Member

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    AFAIK, the block-ends were used on some of the older JTM45, JTM45/100 and JTM50 models
     
  6. valvestorm

    valvestorm New Member

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    The original amp found its way to Dave at LA Sound Designs in LA.
    He has several clips using it on his YouTube channel.


     
    Last edited: May 13, 2018
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  7. neikeel

    neikeel Well-Known Member

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    They do sound good - very organic and you can hear the Hendrix and Trower vibe instantly.
    The block ends were used late 66 and early 67.
    First JTM45 chassis made by Smith’s Industry tended to buckle under the weight of the iron. Mid 67 the steel chassis were brought in.
    I’m running full 560v on mine at the moment with what were new GECs. Very loud for a 45/100 lots of headroom. Screens glow a bit if you put everything on 10, which I know is abuse!
    Might drop it down to the LV taps for a bit. I would use one of the metro virtual variac switches but I do not think that there will be room on the front between chassis and cap board like there is in a 12 series.
     
  8. valvestorm

    valvestorm New Member

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    Thanks Neil! That first amp (the one in the pics/vids) was running 495 at the plates. $$$ NOS GEC KT66 Quad not sure what the preamp tubes were (maybe Harma Retros or the could hav been NOS mullards). I don't have access to the first amp for comparision. The second amp is running 490v at the plates with Harma KT66s and Harma pres. I am look for suggest for any or all of the following:
    1) No easy way to raise the plate voltage, but would it be worth tweaking the downstream decouplers (8.2ks/10ks) to try to get the v1-v3 voltages higher? If so, what would be the target voltages?
    2) What would be an improved tube set for this? v1? v2? v3? What do you guys like in these positions?
     
  9. MarshallDog

    MarshallDog Well-Known Member

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    Very nice looking build! Wish I coukd hear it, bet it sounds great. Is it on the briter side in your opinion?
     
  10. valvestorm

    valvestorm New Member

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    Should be able to hear it in the clips posted a few posts back. I put the bright cap on a pull switch so that it is optional. Pretty sure the clips above were recorded without the bright cap engaged.
     

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