Late '67 Build 100 Watt :) Formerly: Have A Jtm45, Kindly Recommend Me A Jtm50 Version To Build!

Discussion in 'Building the Classics' started by Kats, Mar 6, 2019.

  1. Kats

    Kats Member

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    If I understand you correctly, you’re talking about the green wires from the turret board that will (for eg) attach to pin 2/7 on V1. So once they are hooked it seems to me there is no way to not cross the two wires, but it should only be at 1 point at 90 degrees. What am I missing here?
     
  2. ampmadscientist

    ampmadscientist Well-Known Member

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    Look at the photo I just posted.

    [​IMG]
     
  3. Kats

    Kats Member

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    Holy ampmadscientist, you certainly live up to your name! In a past life you must have been a cheese maker, those braids would make the best mozzarella di bufala the world over!

    bufala1.jpg
     
  4. ampmadscientist

    ampmadscientist Well-Known Member

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    It's not my braids. Originally posted by: http://www.marshallforum.com/members/guitar-rocker.31806/

    This is another example: originally posted by http://www.marshallforum.com/members/coolidge56.55307/

    [​IMG]

    The point was to change the filament layout to decrease buzzing noise.

    The braids is just the builder...whatever.
     
  5. ampmadscientist

    ampmadscientist Well-Known Member

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    When you lay out the grid (pin 2 or 7) like this : "+" with the filament (pin 4/5 or 9), it has a lot more noise.
    Wires are crossed, touching.

    When you lay out the grid and filament like this "=" it has a lot more noise.
    Wires are parallel.

    But if you lay out the filament and grid like this : " I ---- " (90 degrees difference, no crossing) it has a lot less noise.
    Wires are separated and turned 90 degrees from each other.

    filament wirelayout.png
     
    Last edited: Jun 2, 2019
  6. ampmadscientist

    ampmadscientist Well-Known Member

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    Yes I do live up to my name.
    I'm willing to try different ideas, to decrease the noise in guitar amps.
     
  7. Kats

    Kats Member

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    AMS, I totally understand. Please don’t take offence with my sense of humour, I do appreciate all the feedback! The moment I saw the picture, I was reminded of the farms in the Campania region of Italy and eating the cheese so fresh it was still warm. It made me laugh and I couldn’t let it go - I was born this way :)
     
    mAx___ likes this.
  8. Kats

    Kats Member

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    And PS, the pictures of the completed work really does look well done!
     
  9. ampmadscientist

    ampmadscientist Well-Known Member

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    I do a lot of experiments, and it's not meant to be "finished version."

    If the amp is "finished," then it needs to be all pretty and neat I agree. I like it to be all sweet-looking for the customer....
     
  10. Kats

    Kats Member

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    Ahh good news, xformers have shipped and will be arriving in the next few days. In the mean time, what’s up with my bias resistors - what a brain fart. Anyhow now fixed.
     
  11. coolidge56

    coolidge56 Well-Known Member

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    What mad scientist said, noise reduction is cumulative attention to detail can result in a very quiet amp. This photo of mine he posted above, that was a 100 watt plexi and it was dead silent with the volume on 5. On power up I thought something as broken or wired wrong, no just that quiet.

    By the way for that braiding, cut a length of black and red wire. Clamp one end of the two wires to your workbench. Chuck the other end of the two wires into a cordless drill. There go you quick and easy braided heater wire. Someone posted that trick on Metro many years ago.
     
  12. ampmadscientist

    ampmadscientist Well-Known Member

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    And don't forget the screen grid resistors.
     
  13. Kats

    Kats Member

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    8950E37D-6397-42E7-86B3-A5FBAAF822B8.jpeg Forming caps, down to about 35v after an hour. We’ll see how much longer. No black smoke yet :)
     
  14. Kats

    Kats Member

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    Oye, forgot to disconnect CT on PT. Anyhow did so and now measuring 23v after 6 hours.

    Did I cause a problem leaving the CT connected you think?

    Another anomaly I noticed is that the voltage drop across the 100k 2w resistor will drop to 2v if I turn the mains down to 90VAC as opposed to 120VAC. Doesn't that make the 5V or 2V ideal voltage drop a bit arbitrary? Or is something wrong?
     
    Last edited: Jun 20, 2019 at 1:55 AM
  15. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    Why are you reforming capacitors, unless they are old and have been sitting for some time?

    Are the tubes installed during the process?
     
  16. GIBSON67

    GIBSON67 Well-Known Member

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  17. Kats

    Kats Member

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    I thought it would be a good idea. No tubes installed during process. It seems I do have an issue though. The voltage chart turned out good except for v3 where I’m getting 57v on pin 2 93v on 3 and 8 and 60v on 7 (about double the voltage chart for a ‘69 though my build is a late ‘67. But here’s the kicker, when I install the OP tubes and turn mains and standby on there is an UGLY mechanical noise coming out of the OUTPUT xformer.

    Check it out, it sounds like a cow:

     
    Last edited: Jun 20, 2019 at 1:11 PM
  18. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    OP tubes means the four power tubes. I take it you loaded the PI tube in order to measure voltages. Install the other two preamp tubes and remeasure.
     
  19. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    You do have a cabinet hooked up with proper impedance set during all of this?
     
  20. Kats

    Kats Member

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    Yes and yes.

    Load box connected at all times.

    V1, v2, v3 were all installed to make voltage chart. Output tubes were then installed to bias. At this point, as soon as standby was turned on the cow noise began so I shut it down.
     

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