Yes, Another JTM45 Build!

Discussion in 'Building the Classics' started by Chris-in-LA, Jul 31, 2020.

  1. Rotorcraft230

    Rotorcraft230 Well-Known Member Gold Supporting Member

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    Belden RG174-U is a small shielded 26 AWG wire and the OD is .110. Got some of this from Trinity Amps when I built a Triwatt. It’s very nice shielded wire.
     
  2. coolidge56

    coolidge56 Well-Known Member Double Platinum Supporting Member

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    Specs say the RG174-U conductor is copper covered steel.
     
  3. Chris-in-LA

    Chris-in-LA Well-Known Member

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    I finished wiring up the switches and was preparing to mount the last cap can. But I hit a small snag, the holes in the chassis were too close together and too close to the edge. Had to do a bit of drilling. I also added an extra grounding lug to the bolt on the transformer just in case, not sure how I feel about grounding everything to the aluminum chassis.

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  4. Rotorcraft230

    Rotorcraft230 Well-Known Member Gold Supporting Member

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    Ha I had to do the same thing
     
  5. Chris-in-LA

    Chris-in-LA Well-Known Member

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    My choke didn’t fit either, the holes were too close together. You are also using the chassis from Valvestorm, right?
     
  6. Rotorcraft230

    Rotorcraft230 Well-Known Member Gold Supporting Member

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    There too as well. I used a 5/32 chain saw blade file. It is sharp, fine serrations and straight. Works really well for egging out holes. I also have a 1/8” as well for smaller holes
     
  7. william vogel

    william vogel Well-Known Member

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    Most engine blocks and cylinder heads are aluminum today. There’s no problem grounding to aluminum.
     
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  8. Rotorcraft230

    Rotorcraft230 Well-Known Member Gold Supporting Member

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    We don’t have a choice, Helicopters are ALL aluminum.
     
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  9. william vogel

    william vogel Well-Known Member

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    Yep, I don’t worry about the aluminum grounding, I worry about the fasteners being tight enough. The brass hardware scares me for grounding. I use stainless steel hardware for grounding points.
     
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  10. neikeel

    neikeel Well-Known Member

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    Most original chassis were double punched for the internal cap (some use short fat cap, others a longer thinner Hunts/Erie).
    Same with chokes. Original JTM45 and earlt steel JMP chassis were double punched to suit the 20H RS type or the shorter more compact 3H Drake.
     
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  11. Chris-in-LA

    Chris-in-LA Well-Known Member

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    Ok, aluminum is not a problem. Just have to wire the pots and drop in the board and I’m done.
     
  12. Travis398

    Travis398 Well-Known Member

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    I don't know for sure but those ground lugs look coated and are probably rated for aluminum connections.

    I know in the electrical world in most cases they don't have to use noalox (anti oxidation goop) on the aluminum wires connecting to meters and electrical panels anymore.

    it seems they figured out they should make everything rated for aluminum connections.
     
  13. Chris-in-LA

    Chris-in-LA Well-Known Member

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    You’re right, not plain steel, maybe zinc coated, definitely dull gray in appearance.
     
  14. william vogel

    william vogel Well-Known Member

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    Just a recommendation but I always put the screw through the chassis with a star washer and nut then the solder tab and nut. It allows a really nice tightness to the chassis and then the solder tab is easy to position. I ordered lots of hardware from fastenal.
     
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  15. neikeel

    neikeel Well-Known Member

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    I do the same so that the star washer can dig in.
     
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  16. coolidge56

    coolidge56 Well-Known Member Double Platinum Supporting Member

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    I start with a ring terminal...

    [​IMG]

    I remove the plastic, CRIMP it onto the ground wire then solder the ring terminal and ground wire together for both a mechanical and solder connection. Then bolt it to the chassis with #10 stainless screw, star washer, and locking nut. She's well grounded.

    chassisground.jpg
     
  17. _Steve

    _Steve Active Member

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    y
    you make us all look bad ;)
     
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  18. Chris-in-LA

    Chris-in-LA Well-Known Member

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    Good to know, all these different grounding techniques.
     
  19. william vogel

    william vogel Well-Known Member

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  20. neikeel

    neikeel Well-Known Member

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    How are you wiring them?
    What PT are you using (I sold my big RS Deluxe to an Austrailan builder a few weeks ago once I was sure the one in the '65 was fully functional)?
    I presume parallel primaries and secondaries. That means that the 8k transformers will either need to always run two 16ohm cabs in parallel or a suitably rated 8ohm cab? I did the measurements with the variac before dropping tubes in. Other option is two totally separate pairs of tubes with shared HT feed only.
     

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