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Identifying an unmarked transformer.

Discussion in 'Shock Brother's DIY Amps' started by separateness, Sep 23, 2020.

  1. Sep 23, 2020 #1
    separateness

    separateness TDPRI Member

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    Greetings.
    I have in my possession a transformer which I pulled out of an old basketcase Twin Reverb. It was at some point the reverb driver transformer in that amplifier. I would like to use it for an outboard reverb unit I plan on building. The problem is, it does not look like the reverb transformers I have interacted with before and the DC resistances are not what I would expect for the normal 20kΩ:8Ω units.

    The transformer has two sets of leads, blue-blue and white-orange.
    Blue to blue measures ~1.23Ω
    White to orange measures ~548Ω

    The only markings on the case of the transformer is 'T11' on the underside, which sounds like a component number rather than a model number to me. There are no other markings. Is it possible to positively identify this unit? I do not have a signal generator, unfortunately. Looking at the specs of hammond transformers, their 20kΩ:8Ω transformers have a DCR of 1240Ω:0.9Ω. They have a similar model which is 10kΩ:8Ω which has a DCR of 575Ω:0.9Ω. That is pretty close, but is it close enough?

    IMG_9648.JPG
     
  2. Sep 23, 2020 #2
    corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    It's most likely that close enough one - stick your meter leads together when measuring resistance and you'll likely make up the 0.3-0.4 you are "missing"
     
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  3. Sep 23, 2020 #3
    Nickfl

    Nickfl Friend of Leo's

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    DC resistance isn't going to tell you much. You need to measure the winding ratio, which can be done by applying a voltage to one winding and measuring.the resulting voltage on the other winding. The impedance ratio is the square of the voltage ratio.

    More info here
     
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  4. Sep 23, 2020 #4
    separateness

    separateness TDPRI Member

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    If so, that is fortunate as a 10k load is probably a good fit for what I would like to drive it with.

    I realize that, however I do not have a signal generator, as stated above.
     
  5. Sep 23, 2020 #5
    dougsta

    dougsta Tele-Meister

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    You could use a low voltage AC - AC wall wart as a 60hz "signal generator"
     
    Last edited: Sep 23, 2020
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  6. Sep 23, 2020 #6
    Djentleman Dan

    Djentleman Dan Tele-Holic

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    upload_2020-9-23_10-22-4.png
     
  7. Sep 23, 2020 #7
    separateness

    separateness TDPRI Member

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    You know, I had not considered this. I think I have a 12VAC wall wart I wanted to use for a small tube power supply somewhere. I will see if I can find it.
     
  8. Sep 23, 2020 #8
    corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Let's not confuse "signal generator" and "voltage generator" here either, even though they can be the same device in some cases :D
     
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  9. Sep 24, 2020 #9
    dougsta

    dougsta Tele-Meister

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    For safety, make sure you input the 12v ac to the primary winding, it will be one with the higher dc resistance, if you input to the secondary you might expose yourself to, eg a 40:1 ratio will give approx 420v ac!
     
  10. Sep 24, 2020 #10
    dougsta

    dougsta Tele-Meister

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    Hence the quotation marks! Maybe he could request the electric company to do a 30hz to 15khz sweep on the line voltage they supply :lol:
     
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  11. Sep 24, 2020 #11
    separateness

    separateness TDPRI Member

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    Welp, I ended up taking it to the electronics shop at my job and it seems to have a winding ratio of ~18:1 and an impedence ratio of ~360:1. This would put a reflected 8ohm load at 2.88k. I have no idea how the previous user was driving this with a paralleled 12at, or with what I could drive it sufficiently. Back to the drawing board, I reckon.
     
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