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50's Power Transformer for Tweed Champ, 18w Marshall, or Deluxe?

Discussion in 'Shock Brother's DIY Amps' started by Ronno25, Feb 24, 2021.

  1. Ronno25

    Ronno25 TDPRI Member

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    The high end was fine with the original PT. If I end up keeping this one I may try that mod though. Thanks for the heads up!

    Is there a reason the resistor isn't soldered directly to the pin on the socket?
     
    Last edited: Feb 25, 2021
  2. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    None I know of.
     
  3. Ronno25

    Ronno25 TDPRI Member

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    Any ideas why I'm getting such a bad 120hz hum with this old transformer? I've tried grounding the high voltage center tap in a few places including two different transformers bolts and the ground rail on the board. I haven't changed anything else except the transformer. This transformer has no center tap for the heater secondary but I've installed (2) 100ohm resistors from pin 2 to 8 and from pin 7 to 8 on V3. Could it be a bad transformer?
     
    Last edited: Feb 26, 2021
  4. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Sometimes the old transformers have a CT wired to the frame of the PT. Let's cross our fingers.
     
  5. Ronno25

    Ronno25 TDPRI Member

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    I'm not quite sure what you're referring to but I examined the outside of the transformer frame and there is nothing there indicating a wire or anything like that.

    When I originally removed the transformer from the radio I did note that one of the green AC wires was connected to the power tubes and the other was connected directly to ground. It seemed notable but I didn't (and don't) understand why this was done. Could this be the source of my issue? I'm kind of shooting in the dark here.
     
    Last edited: Feb 26, 2021
  6. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Sometimes a CT is connected under the bell cover to the body of the PT. When the PT is bolted down the CT makes contact with the chassis. If an artificial CT is then connected there will be humm. Disconnect the artificial CT and use your meter and measure for continuity or some small resistance from the secondary wires to the body of the PT.
     
  7. Ronno25

    Ronno25 TDPRI Member

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    I disconnected the artificial center tap and powered up. Same amount of hum, or worse? Any more ideas before I scrap it and put the original PT back in?

    Thanks to all!
     
  8. 2L man

    2L man Tele-Meister

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    Transformers radiate an electromagnetic field which strength and pattern depends of its construction. There are few articles on internet and discussion too on various forums.
     
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  9. Ronno25

    Ronno25 TDPRI Member

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    I just wanted to follow up here with a question if someone will entertain me. I'm still wondering about the problem with loud hum and buzz when this power transformer was installed in my 5e3. I would really like to use this transformer in a build. So I'm wondering, is this thing outright broken or is there a solution?

    I know the radio the PT came out of had it wired with one heater to the filaments and one heater to ground.

    I'm wondering if wiring the PT the same way as in the original radio would fix the hum/buzz issue.

    I did try an artificial center tap with the transformer, which did not resolve the issue.

    Anymore advice/info would be greatly appreciated! Thanks in advance.
     
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