/ Register

  1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

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

    Age:
    36
    Posts:
    85
    Joined:
    Dec 12, 2019
    Location:
    South Carolina, United States of America
    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

    Posts:
    4,620
    Joined:
    Sep 13, 2008
    Location:
    Lansing, MI
    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"
     
    separateness likes this.
  3. Sep 23, 2020 #3
    Nickfl

    Nickfl Friend of Leo's

    Posts:
    2,489
    Joined:
    May 24, 2016
    Location:
    Florida
    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
     
    mojek likes this.
  4. Sep 23, 2020 #4
    separateness

    separateness TDPRI Member

    Age:
    36
    Posts:
    85
    Joined:
    Dec 12, 2019
    Location:
    South Carolina, United States of America
    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

    Posts:
    193
    Joined:
    May 25, 2015
    Location:
    Edinburgh, Scotland
    You could use a low voltage AC - AC wall wart as a 60hz "signal generator"
     
    Last edited: Sep 23, 2020
    mojek and separateness like this.
  6. Sep 23, 2020 #6
    Djentleman Dan

    Djentleman Dan Tele-Holic

    Posts:
    907
    Joined:
    Jul 30, 2018
    Location:
    Moorpark, CA
    upload_2020-9-23_10-22-4.png
     
  7. Sep 23, 2020 #7
    separateness

    separateness TDPRI Member

    Age:
    36
    Posts:
    85
    Joined:
    Dec 12, 2019
    Location:
    South Carolina, United States of America
    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

    Posts:
    4,620
    Joined:
    Sep 13, 2008
    Location:
    Lansing, MI
    Let's not confuse "signal generator" and "voltage generator" here either, even though they can be the same device in some cases :D
     
    Nickfl, Wally and dan40 like this.
  9. Sep 24, 2020 #9
    dougsta

    dougsta Tele-Meister

    Posts:
    193
    Joined:
    May 25, 2015
    Location:
    Edinburgh, Scotland
    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

    Posts:
    193
    Joined:
    May 25, 2015
    Location:
    Edinburgh, Scotland
    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:
     
    corliss1 likes this.
  11. Sep 24, 2020 #11
    separateness

    separateness TDPRI Member

    Age:
    36
    Posts:
    85
    Joined:
    Dec 12, 2019
    Location:
    South Carolina, United States of America
    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.
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.