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adjustable shielded coil pins?

Discussion in 'Electronic Basics' started by tylerz, Jul 10, 2004.

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  1. tylerz

    tylerz Guest

    Hi I have searched the net everywhere for this basic question, but nothing
    turned up. I have some adjustable shielded coils (the little square packages
    with the bobbin inside), which have 5 pins coming out of the bobbin and 2
    pins due to the shield. Pulling it apart it has wires coming from the coils
    to all the pins. This made me believe that it was a transformer of some
    kind, which is what I want. So, I intended to test this to see if I could
    induce a votage from one set of pins to the other by hooking a digital
    voltmeter to one set of pins and switching power on and off to the other set
    of pins. I tried a 1V to a 9V and never see any induced voltage.

    So my questions are:

    What is the standard pin layout of these types of inductors/transformers?
    Are they meant to induce voltage from one coil to the other when all 5 pins
    are connected to the coils?
    Is my testing appropriate and if not what is the simplest way of testing

    Thanks for any assistance offered,

  2. Hi,
    There isn't one really, just dozens of variations on a theme. Assuming that
    the item you have is an RF transformer, try a search for TOKO inductors (a
    very common make) and see if any of the basing diagrams fit your transformer.

    With five wires it is probable that there are two windings with one of them
    being tapped. You can find plenty of these on old transistor radios in the
    form of IF transformers tuned to either 10.7MHz or 455kHz depending on whether
    the set is for FM or AM.
    If it indeed has two windings, then you would have to connect your voltage
    across one winding and detect the induced voltage across the other - that is,
    a minimum of four wires. If it were a tapped winding however, then one wire
    would be common to both and only three are needed.
    Your problem would be the response time of the DVM. The most that you are
    likely to see is a slight twitching of the digits. To do this properly you
    really need an analogue meter or an oscilloscope with a reasonably fast
    timebase but a slow speed screen such as in a storage scope.

    Try finding a mains or an audio transformer, since these have a much
    greater mutual inductance, and borrow an analogue meter from somewhere (they
    are much better for some things) and try again to rediscover Faraday's laws
    that way.

    All the best - Joe
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