[AMRadio] Transformer

gkb gkbrown at gwi.net
Thu Feb 1 16:52:05 EST 2007

    If you have access to a hypot tester do a test at twice the secondary
voltage plus a thousand. This is a good rule of thumb. With the resistance
measurements your getting, I would sure bet it will fail the hypot test
before it even gets to a couple of hundred volts. One other thing, if you do
bake it, let it cool down slow. This way it will not suck moisture back into
the core and add to the problem.
    This is an old transformer and insulation is just not holding up
anymore. The older magnet wire was covered with varnish or a form of older
formvar and probably just single layered. This insulation was only good for
about 110 C. The new, double insulated magnet wire is good for 155 C and the
triple coated is good for 200 C.
    Just some thoughts.
----- Original Message ----- 
From: "Rick Brashear" <rickbras at airmail.net>
To: "Discussion of AM Radio in the Amateur Service"
<amradio at mailman.qth.net>
Sent: Thursday, February 01, 2007 4:30 PM
Subject: Re: [AMRadio] Transformer

> Thanks John.  Yes, it is a plate transformer.  I'm afraid it's in
> trouble, but I am going to try baking it and running some serious tests
> before I commit to the money it will take to rewind or replace it.
> I appreciate the advise,
> Rick/K5IZ
> John E. Coleman (ARS WA5BXO) wrote:
> >Rick
> > Is this a plate XFMR?
> >If it is a plate transformer, then 50,000,000 ohms is a lot of resistance
> >for 117 volts.  The leakage current would be a about than 2 micro amps...
> >
> >
> >
> >
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