Output Transformer Wiring Question

Discussion in 'Shock Brother's DIY Amps' started by TobyZ28, Jan 28, 2020.

  1. TobyZ28

    TobyZ28 Tele-Meister

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    Hi all, I have a yellow wire coming out of the output transformer (along with the green and black wires). Is this a centre tap? What is the best thing to do with it as I have no reference to it in my schematic (Cover the end up with ShinkWrap/other)?

    The schematic I "thought" was for the output transformer only shows a black and green wire coming out as well, no yellow.

    Thanks in Advance...
     
  2. schmee

    schmee Poster Extraordinaire Silver Supporter

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    It's likely a multi tap tranny. What brand?
     
  3. Lowerleftcoast

    Lowerleftcoast Tele-Meister

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    If there is no data on the OT. I have a NIB multi tap 18watt 4,8,16 ohm. If you want to take resistance readings green to black and yel to blk, we can compare. Maybe you can figure what ohm speaker works with the green/blk and yellow/blk.
     
  4. Lowerleftcoast

    Lowerleftcoast Tele-Meister

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    Assuming it is a multi-tap OT, I would wire it like a hot rod deluxe. Or similar.
     
  5. dan40

    dan40 Tele-Afflicted

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    Those colors are generally associated with the OT secondary which connects to the speaker. As the fellas pointed out, a few resistance readings will help to determine which tap is which. The black is most likely the common which goes to the sleeve of the output jack.

    The OT primary should also be three wires. One goes to B+ and the other two go to each 6v6. A resistance reading will also help determine which ones to use there.
     
  6. schmee

    schmee Poster Extraordinaire Silver Supporter

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    "(Cover the end up with ShinkWrap/other)?" ....short answer, yes, cover up the end of the tap you are not using.
     
  7. TobyZ28

    TobyZ28 Tele-Meister

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    The ohms on the OT input side are:
    • Brown-Blue 538 Ohms
    • Red - Blue - 274
    • Red - Brown - 264
    The output side was bouncing around 0.1 and 0.0 for all three combinations, I don't think my Klein multimeter goes any lower. I do have a low current 120-20v AC transformer I can wire up. Would it make sense to wire this up to the Brown/Blue wires and measure the voltages between the Green/Black/Yellow output wires or will this roast the transformer :D?
     
  8. TobyZ28

    TobyZ28 Tele-Meister

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    I went ahead and did the test. Step in if i'm mathing it wrong, this is a total noob amp math attempt!
    Input Voltage to Brown/Blue leads: 19.4V (RMS)
    Output Voltage:
    • Blue/Green - 0.72V
    • Yellow/Blue - 0.5
    • Yellow/Green - 0.21
    Overall Step Down Multiplier:
    19.4/0.72 = 26.66x

    So say I have 350VAC going in through the Brown and Blue leads...
    350V/26.66 = 13.12 VAC out (?)

    I have no clue how this translates into what kind of speaker to hook up or what the yellow wire is for :D.
     
    Last edited: Jan 28, 2020
  9. Lowerleftcoast

    Lowerleftcoast Tele-Meister

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    Blue/Green - 0.72V = 8ohm
    Yellow/Blue - 0.5 = 4ohm

    Some options:
    Shrink wrap yellow
    Wire in a switch for 8ohm and 4ohm selection
    Buy a switching jack and wire it like a hot rod deluxe

    If you will not be running an extension speaker, just shrink wrap the yellow. Leave it long. It can be used for negative feedback at a later time, if so desired.
     
  10. TobyZ28

    TobyZ28 Tele-Meister

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    Perfect, will do!
     
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