Not another JTM45 build!

Discussion in 'Building the Classics' started by jessemhopkins, Jul 26, 2020.

  1. neikeel

    neikeel Well-Known Member

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    Is Chris doing the RS OT again? He stopped offering them for a while (I thing there was a problem with lamination supplies?).
    I used a Marstran RS in my split front clone and made a paxolin turret board instead of wires.
    [​IMG] [​IMG]
    Sorry about the photobucket smear!
     
  2. jessemhopkins

    jessemhopkins Member

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    Yep, that’d be it. I’ll snag one, thanks! Been struggling in my head about how I’m going to modify the chassis in order to make everything fit, but I think I just figured it out. This forum and everyone’s help has been a godsend!
     
  3. Amadeus91

    Amadeus91 Well-Known Member

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    No Neil, he is still not making them.
    This one was purchased years ago and is from my spare parts inventory.
    Went with a real RS OT instead.
     
  4. jessemhopkins

    jessemhopkins Member

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    [​IMG]

    Curious what the group's take is here. I finally got my ot from Merren and enlarged the opening for the pt so this one will fit. Upon dry fitting, I discovered that they are right on top of each other. Is that concerning?
     
  5. neikeel

    neikeel Well-Known Member

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    They do look a bit closer than normal.
    Can you oval the PT holes to nudge one way and the OT the other way?
    You might get 5mm extra clearance that way.
    How big is the Merren PT?
     
  6. jessemhopkins

    jessemhopkins Member

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    I can move the ot, not the pt. It's this chassis, they layed it out so horribly!
     
  7. jessemhopkins

    jessemhopkins Member

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    Well, I have finally concluded that this Mojotone chassis isn't going to work. If I were using the Mojotone iron (Heyboer) it'd be alright but with the bigger Merren iron there are too many issues. Looking for suggestions for an offset chassis, but I may wind up using a blank and punching everything out myself.
     
    neikeel likes this.
  8. Chris-in-LA

    Chris-in-LA Well-Known Member

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    Both my JTM45 kits have 270k mixers and sound pretty good. But the Ceriatone kit has a 100pf treble cap and it has more sizzle than the Valvestorm kit, which has a 500pf cap. I also have two tweed Super kits with 100pf treble caps. Would going up to 500pf on these kits reduce some of the high end sizzle? @neikeel
     
    Last edited: Oct 29, 2020
  9. jessemhopkins

    jessemhopkins Member

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    Well gang, a million months later and I'm finally getting started. I was hoping for some input from those of you who have used Merren transformers before, I don't have a wiring diagram for the OT so I'm a little in the dark about which color is which. Looking at it with a friend, we worked out that the white/brown/red side is the primary and the green/orange/yellow side is the secondary, and that on the secondary either the green or orange is the common. Can anyone confirm? I'm going to try to phone Chris Merren in the morning but he's been a bit tough to track down, so if one of you knows it would be a huge help.

     
  10. william vogel

    william vogel Well-Known Member

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    Primary:
    Brown is the center tap, hook it to the B+
    Red goes to V4 plate
    White goes to V5 plate

    Secondary:
    Yellow 0
    Orange 8 ohm
    Green 16 ohm
     
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  11. jessemhopkins

    jessemhopkins Member

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    Ace! Thanks so much
     
  12. william vogel

    william vogel Well-Known Member

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    You’re welcome
    Just FYI
    Chris used to use a black wire instead of the white just like an original drake 784-103 but he quit buying the black wire and if it had a blue wire it would be the 100 volt line tap. You’re really going to like the transformer, I’ve used many of Chris’s transformers.
     
  13. jessemhopkins

    jessemhopkins Member

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  14. jessemhopkins

    jessemhopkins Member

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  15. william vogel

    william vogel Well-Known Member

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    Just wondering why you started with green wire. I get it when the power transformer has green flying leads but you’ve got a Merren with solder lugs.
     
  16. jessemhopkins

    jessemhopkins Member

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    That's a great point, I didn't even think about it. I just started following the Metro pdf. Oh well, it's done now. I won't be that muck of a stickler.
     
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  17. jessemhopkins

    jessemhopkins Member

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  18. Chris-in-LA

    Chris-in-LA Well-Known Member

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    Bluesrock and Far Rider like this.
  19. StuC

    StuC Member

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    Wire it the same way as the later JTM45s: choke and centre tap of the OT to the corner turret on the board, and run a separate wire from there to the filter cap.

    Edit: obviously, if you do this, angle the bias diode over to the next turret and don't link those two end turrets.

    [​IMG]
     
    Last edited: Dec 30, 2020
    adew1 likes this.
  20. william vogel

    william vogel Well-Known Member

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    ^^^^^^THIS
    I wire all plexis this way. It gives you a good point to measure B+ too.
     

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