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Are these transformers faulty?

Discussion in 'General Electronics Discussion' started by ecollen, Nov 7, 2015.

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  1. ecollen

    ecollen

    84
    13
    Jul 31, 2015
    Hi,
    Carrying on from my previous enquiry about making a little 2-transistor amplifier for my crystal set

    Audio transformer for crystal set help

    I have got hold of a few audio transformers, and I have one that I think will work, a 1K5-180E (by the way, what’s the E for?). My original instructions asked for a 8 ohms to 1 k.

    I also have 2 other transformers, called 1K to 150E, but I’m wondering if these 2 are faulty. I used my DMM to check the resistances across the leads. Can one check transformers in this way?

    In any case, on one of them on the tapped side (call the leads 1, 2 and 3), I get 66 ohms between 1 and 2, but zero between 1 and 3 as well as between 2 and 3. On the untapped side I get 859 ohms between the leads.

    On the other one, I get readings between the leads on the tapped side, but zero between those on the untapped side.

    Does this mean they’re faulty, or can’t they be checked like this?

    Thanks,

    Errol

    Add: Sorry, I don't mean "zero", I mean I get no reading, no response from the meter.
     
    Last edited: Nov 7, 2015
  2. Technician Tonny

    Technician Tonny

    34
    2
    Aug 31, 2015
    Hi Ecollen
    You can check the transformer in that way when defferentianting between the primary and the secondary parts

    The primary part is used as the input in stepdown transformer's
    and the secondary part is used as the output
    e.g 240VAC primary to 12VDC secondary

    There are many types of transformers with deferent functions and different ways to test them (ohms testing and voltage testing etc..)

    Your transformers may not b fault...
    What type of transformer shown in your two transistors amplifier? is it a voltage supply T or!!!
     
    ecollen likes this.
  3. ecollen

    ecollen

    84
    13
    Jul 31, 2015
    Hi Technician Tonny

    Many thanks for your reply.

    No, it's an audio transformer. Here's the schematic.

    I'm glad to hear you say the transformers might not be faulty. I was planning to contact the supplier tomorrow and ask to send them back, but I'd prefer not to have to do that, and I'm really not sure. It's just that from those tests of mine I THINK they're faulty, but I don't have any specialist knowledge.
     

    Attached Files:

    Technician Tonny likes this.
  4. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    When you say you get zero, do you mean there is no connection or there is a connection but zero ohms?
     
    ecollen likes this.
  5. Bluejets

    Bluejets

    4,161
    882
    Oct 5, 2014

    Attached Files:

    ecollen likes this.
  6. ecollen

    ecollen

    84
    13
    Jul 31, 2015
    Hi Duke

    Apologies, yes, I mean when I connect the meter there is no response. As Bluejets says, it appears to be an open circuit
     
  7. ecollen

    ecollen

    84
    13
    Jul 31, 2015
    Hi Bluejets

    Thanks for your reply, and for the link. That's in fact exactly what is specified in my instructions "1 k centre tapped to 8 ohms". I couldn't find one anywhere though and have been trying to get something else to make do. Perhaps I'll try to order some from Jaycar. The only problem is that overseas orders take forever to get here, if they ever do. But it's worth a shot.

    E must mean ohms, yes, thanks. I wonder why.

    What also worries me is that I have no way of measuring impedance, so I don't know if my resistance measurements give me any meaningful readings. It does seem odd though that some of the resistance readings appear to signify an open circuit. Yes, I'll have to contact the local suppliers. What's the bet though that they'll say they don't know :) Maybe I should just buy half a dozen of the things and keep trying them until I find one that works.
     
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