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Reading Transformer.

  1. Jul 7, 2012 #1
    I was just curious if anyone could point me in a direction on how to read transformers that are not industrial transformers? I ask this because I'm new to the field of electronics and I found an old transformer from my grandfather and the only information written on it is PT-54-A next line B1-00354F. I've been searching online for tutorials on how to read the nameplates of transformers but nothing of value has turned up. I tried searching with just PT-54-A and nothing came up at all. Thank you for your time.
  2. jcsd
  3. Jul 8, 2012 #2

    jim hardy

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    start by making yourself a drawing of which wires are on individual windings.

    That you do with an ohm-meter, and be sure to write down how many ohms . That'll let you identify windings that have taps. You'll need a good meter with RX1 scale.
    Some DMM's freak out when tying to measure a highly inductive winding, you may have to get creative. This is one application where analog meters often excel.

    Lastly check for an intentional air gap in the core laminations. If there's one big enough to see, you might have an inductor choke not a transformer.

    old jm
  4. Jul 8, 2012 #3


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    Many old radio transformers will have filament windings which were typically 5 volts, 6.3 volts or 12.6 volts.

    These are usually thicker wire than the primary or high voltage secondary wires.

    If there are windings like this, you can connect a different source of 6 volts (AC) to them (one at a time) and measure the voltages produced on the other windings. Don't touch any windings with your fingers while you do this.

    This may give you an idea of the other voltages needed or produced by the transformer.

    If it is a radio transformer, it will probably have a high voltage winding that is center-tapped and produces about 700 volts across the whole winding. It will also have a primary winding that is intended for your mains voltage. This may have several tapping points near one end for slightly different mains voltages.

    The model numbers of these transformers probably don't mean much as the original factory may have closed down many years ago.
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