[Hallicrafters] HT-37 low voltage rectifier

[Roger(K8RI)]

> Hi Riley,
>
> The buzz is most likely coming from loose laminations in the transformer.
> This is brought about by the increased load of the rectifier filaments
which is
> why it s\disappears when you go solid state. You can try to tighten up the
> bolts holding the transformer together.  This sometimes helps, but does
not
> always work.  If you have a horizontally mounted transformer, you will
have to
> loosen the mounting bolts below the chassis and use an ignition wrench
above the
> chassis to tighten the bolts, then retighten the below chassis hardware.

I know a ham who lives in Saginaw that used to vacuum impregnate
transformers using transformer varnish, a heavy walled 5 gallon bucket, a
vacuum cleaner, and much to his wife's displeasure, her kitchen oven to dry
the thing once done.  I don't know if he's still married or not.

It was a simple process.  Put the transformer in the bucket. Pour in enough
varnish to cover the transformer by a couple inches.  Hook the vacuum
cleaner to the top of the bucket (he had soldered a fitting on the lid), run
the vacuum cleaner for 15 minutes or so, to get the air out of the
transformer, then disconnect the vacuum cleaner which let the air back in
the bucket which forced the varnish back in between laminations and
windings. Let drip for a few minutes, place in oven over cookie sheet (for
obvious reasons) and bake till dry.

It was not a high vacuum, but according to him it worked quite well even if
it was messy (and smelled up the whole house)

Roger Halstead (K8RI, EN73 & ARRL Life Member)
N833R, World's Oldest Debonair? (S# CD-2)
www.rogerhalstead.com.
>