"Steven P. Burrows" wrote in message
news:MDF9e.3514$lz1.2504@lakeread01...
I am restoring a couple of S-40B receivers, and I am interested in finding
a
replacement power transformer. The transformers that came with the radios
appear to have moisture in them, probably from years of storage in a humid
environment. The one transformer that I have tried to power up on a
variac
started to sizzle when I got to 50 VAC on the primaries, so I powered
down.
I plan to attempt to dry out the old transformers, but I would prefer to
replace both with new, known to be good units.

I have looked over the offerings from Antique Electronics Supply, and
their
Fender transformers are a close match. Unfortunately, the Fender
transformers offered there top out at 325-0-325 V for the secondary
windings. I need a transformer with 350-0-350 V / 70 mA, 5 VAC / 2A, and
6.3 VAC / 2.6A secondary windings.


The difference between 325V and 350V isn't much. I can't think of a single
reason why the radio wouldn't perform well if the plate voltage was reduced
by less than 10%. If you're really worried about the 25V, you could
probably get it back if you used a solid state rectifier rather than the
tube rectifier.



sealing them in an airtight
container with silica gel for a dessicant, for about a week to ten days.
I
have read of techniques for drying out transformers that involve running a
low DC voltage in the primary for several tays to heat up the transformer
so
that the water could be cooked out. The risk of arcing and/or
electrolytic
corrosion makes this approach seem risky to me. I am not particularly
interested in setting up an oven to passively dry out these things, so a
chemical dessicant seemed a reasonable approach. I work in a university
chemistry department, so if I can find some sort of vacuum chamber, I
might
try to remove the water that way also.

If the power transformer is moisture damaged, there might be more damage in
the IF transformers and RF coils. These are common radios. You might want
to consider the unknown costs and potential problems in fixing up these
radios as compared to simply recapping and checking the resistors on a known
working S-40B.


ement that a prior owner used (vinyl covered
wire leads vs. cloth covered in the radio). I have two other transformers
that are original Hallicrafters units, but given their age I am not
optimistic about them.

If the transformers work, they should at least be good for bench testing the
radios.


One of these radios is a gift for my father, so I would prefer a "new"
replacement transformer that I don't have to worry about leaking current
or
eventually going up in flames.

Thanks in advance for any suggestions or ideas that can be offered

Steve Burrows




Good luck!

Frank Dresser