[AMRadio] Seeking advice on testing modulation transformers

Todd, KA1KAQ ka1kaq at gmail.com
Thu Sep 21 10:12:00 EDT 2006

On 9/21/06, Mark Foltarz <Foltarz at rocketmail.com> wrote:
> Todd,
>   Yes, a good point.
>   I also found some other transformers of interest including four  nos RCA
> transformers that use PP parallel 807 for  an audio amplifier  application.

You have some nice sounding iron in your pile of 'stuff'. I have a
beautiful old Thordarson MultiMatch 500w mod transformer with the nice
end bells and black wrinkle paint that I want to use in a HB rig
someday, but I hate to hide it inside where it can't be enjoyed

>   So how would you dry out old transformers?

Well, being single is really great in cases like this or baking
painted items. I have an old General Motors Electric range in the
kitchen that doubles as a radio assistant for such things. I remove
all but one rack and set it to 120 degrees (which is proably closer to
150, electric ranges being what they are) and bake away. If it's a
painted item, I crack the front double doors just a bit to help it
outgas. For transformers, I keep it closed for a while to let the heat
build up and penetrate the iron, then crack the doors. Times vary.
Painted things, 20 minutes to an hour; iron, 30 minutes to several
hours, depending how large it is and where it's been stored.

The trick to baking until you get a handle on how your range works is
to keep watch to make sure it doesn't so hot as to melt any potting
compound. I try err on the side of caution by keeping the heat lower
and increasing if needed. The downside is, you need to bake it longer.
Upside is, no tar ooze. I've heard from guys in TX, AZ and other hot
places that they just sit their iron in the sun on a hot summers day
and let it cook away. Not sure how that would work in FL due to the

Of course, it won't be as easy to pull off using the range when
married. I think you got hitched last year IIRC? My time is coming one
month from today. She's okay with my radios, but I think it will
require a 220 outlet in the garage with a old electric range devoted
to just such things. I'll let you know when something is hooked up and
you can tool over to my place. We'll probably be up north of Tampa in
Pasco county somewhere.

I think Don Chester has a way that involves running voltage through
the transformer at a reduced level, to heat it up. Others use boxes
with light bulbs inside. Maybe they'll chime in with additional

~ Todd  KA1KAQ (soon to be a 4-Lander)

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