JTM45 Build thread

Discussion in 'Amps and Cabs' started by big mike, Apr 30, 2014.

  1. zzmoore

    zzmoore Member

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    Let me see if I can my borrow back my Thro Bak (St)Range Master from my friend.....
     
  2. big mike

    big mike David Grissom Wannabee Gold Supporting Member

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    No worries Chip...i may use it as an excuse to nab a beano boost or an astrotone from analogman...
     
  3. ScienceFriction

    ScienceFriction Member

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    ..and a pair of alnico Celestions. :rockin
     
  4. zzmoore

    zzmoore Member

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    No Prob.....maybe BYOC...in keeping with the shoestring budget. ;)
     
  5. big mike

    big mike David Grissom Wannabee Gold Supporting Member

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    Thought about that but hbe germanias seem to go used on ebay for the cost of a byoc kit.
    Joel's pedals are killer.
     
  6. Hacksaw

    Hacksaw Time Warped Gold Supporting Member

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    Hey Big "Country" Mike, < nice ring to it!

    Amp sounds great!! Are you still planning to build the head shell?
     
  7. big mike

    big mike David Grissom Wannabee Gold Supporting Member

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    May drummers building it...he's a carpenter. Modeling after my 50 watt but narrower side to side.


    Finish will be a surprise.....
     
  8. woof*

    woof* Member

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    Sounds great mike! Yeah stick a boost or drive in front!
     
  9. big mike

    big mike David Grissom Wannabee Gold Supporting Member

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    Posted this in the nos tube bitchfest..but updating here.

    Did toss some of my NOS/ANOS stash in my recent JTM45 build last night, I run that clean. It had worn and used GT pulls for break in.
    Just grabbed what was on the tp of my tube box.
    Westinghouse somethingn or other V1
    GE JAN 12ax7 V2
    Sylvania Baldwin pull for V3.

    Subtle changes...not DRASTIC but definitely more defined and detailed..but again, mostly clean, I use that amp with pedals where the difference again is less noticeable...but I won't likely change them again for 5 years plus...

    Due to the generosity of another member I have a quad of RCA 6L6 pulls to see if I can match up a pair for this and remove the 10ma apart tungsol reissues....
    __________________
     
  10. billstets

    billstets Member

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    Hey Big Mike, your build sounds awesome!

    I built a Metro JTM45 kit about 6 years ago and based on recommendations from some guys on the Metro Amp Forum, I made some modifications over the years. I'm loving the amp and it seems much more JMP-ish to me, without losing all of the JTM45 charm. The bass isn't as boomy (or flubby with gain) and overall the amp just sounds better to my ears. I have a recording from a field recorder at our last gig and I'm floored at how great it sounds. I made the following mods; do you think that these make it a little more JMPish?

    Marstran PT - the original Heyboer put out B+ in the 300s, I'm getting well into the 400s now.
    .0473 PI coupling caps instead of the .100s
    470K mix resistors
    100pf cap on the HT volume, instead of the 500pf

    In addition to a great lead tone nudged with a TS808 as a boost, it has a beautiful clean tone and I can get a really nice touch sensitive Marshall crunch sound. In other words, if I pick moderately it's beautiful clean and then if I hit some power cords or open chords hard, it really barks and has a nice Marshall kerang thing going, to my ears anyway. Of course I don't have a JMP to compare it to. I owned one many years ago.
     
  11. big mike

    big mike David Grissom Wannabee Gold Supporting Member

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    We're pretty close there.
    I got 400V on my last JTM45 Rectified..

    This one with the classictone gets in the 414 range.

    I've been a 100pf brite cap user for a long time.
    470K mixers make it more bass spec ..I did that before as well,but you lose the JTM Cleans with that mod.

    the 'mid way' point coupling caps are a good mod, I've done that a lot.
    I also generally (and I think in this one too) did a 100pf fizz cap instead of 47pF....
    reason being it takes a touch of the high end off there...just smooths it out.
     
  12. billstets

    billstets Member

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    I thought the 1987s also had 470k mixers, no?
    When you say fizz cap, you're referring to the mixer cap right?
     
  13. big mike

    big mike David Grissom Wannabee Gold Supporting Member

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    ALL later amps have 470K mixers. It's about the same time the amps changed from JTM's to JMP's.

    all of em. 50 watters and 100 watters, bass or lead. The mix resistors don't define lead or bass. (1986 or 1987/1959 or 1992).

    No, not the mixer cap...I usually leave that at 500 (470) but you can tune the amp using different volumes there as well.

    The fizz cap is in the PI. It's the small 47pF cap that connects the 2 PI plate capacitors at the top of the board.

    Below is a 'named' JTM45 board layout. It's the phase inverter capacitor.

    Depending on if you want to add gain or not, or mid boost you can add caps and change values at V1 and V2 as well. But the more you mod, teh farther away it gets from that JTM45 tone.

    [​IMG]
     
  14. billstets

    billstets Member

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    Thanks. I thought you said the 470 mixers were more bass spec. Yeah I don't think I'll mod any more. It sounds great!
     
  15. ScienceFriction

    ScienceFriction Member

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    Mike, how are you liking the tube rectifier at this point? Does it give you a clean character that you enjoy more, or does it really not make a big impact at that stage? It's been a long time since I played an amp with a tube rectifier, but knowing how you feel about them I was wondering how you are getting on with it. Have you cranked it up much yet?

    Speaking of builds.. I sent my JMP50 build to FusionBear for some servicing, as I wanted someone to look over it, and he's sending her back with a clean bill of health. I never did spend much time with it so I'm really excited to put it through its paces. I still want to try a JTM45 at some point. I like what you did here and have often though about building another Marshall- like a Radiospares JTM45. Something for straight up killer cleans.
     
  16. Stu Blue

    Stu Blue Member

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    Actually RCA 6L6s were my favourite in my old JTM45 (I think about 430volts B+ might have been 440 I haven't checked for years).... but mine is pre KT66 with the valve bases too close together for KT66s (they almost touch).

    EDIT For financial reasons I use JAN Phillips 5881s now.
     
  17. big mike

    big mike David Grissom Wannabee Gold Supporting Member

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    Science... I so feel some sag even low...it's not that immediate whoomp a jmp has it's softer under the fingers a touch I think that may be more about the low filtering though.

    [​IMG]
     
  18. Sirloin

    Sirloin Supporting Member

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    Sweet amp ya got there sir!
     
  19. Hacksaw

    Hacksaw Time Warped Gold Supporting Member

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    Check out the headlights on that gal! sweeet!
     
  20. big mike

    big mike David Grissom Wannabee Gold Supporting Member

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    You da man hacksaw..
    Got a pair of them with in 4ma. Sound killer.
    The other are about 10 apart...maybe a cathode bias amp?
     

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