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.

I would also be interested in finding out a place to send the old
transformers for rewinding if nothing is available for replacement.

Meanwhile, while I search for replacements I plan to attempt to dry out the
old units by removing their shell covers and 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.

The sizzled transformer mentioned above was not an original Hallicrafters
unit, but some sort of replacement 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.

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

"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

That transformer with the 325-0-325 volt secondary will work just fine.
Put it in and don't look back. With today's higher line voltages, I
suspect the B+ voltage will be very close to spec. Exact B+ isn't that
important anyway.

Best Regards,
Ed

Steven P. Burrows wrote:

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.

Go with the Fender, and see what the actual operating voltages are. I
suspect that the output of the Fender transformer will be higher than
rated if they are operated below full rated load.

If the B+ is not in the correct range with the new transformer, swap
the rectifier tube out for silicon. You'll gain probably more than 25V
in the process.

I would also be interested in finding out a place to send the old
transformers for rewinding if nothing is available for replacement.

Peter Dahl Co. in Texas will rewind them, and they will also probably
be willing to build you a new one that is a better match for the original
Hallicrafter part. They might even have the drawings for the original,
even. They will charge a lot of money, but their work is magnificent
and as far as I can tell their rebuilts are far more reliable than the
original windings.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

In article MDF9e.3514$lz1.2504@lakeread01,
"Steven P. Burrows" wrote:

(Damp transformer insulation)

Meanwhile, while I search for replacements I plan to attempt to dry out the
old units by removing their shell covers and 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.

That's really only for oil-cooled transformers in electricity substations,
where you had to get *all* the moisture out of the (paper) insulation
before filling with oil or bad things happened when you applied power.

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.

Keeping it in a warm/hot place, sealed up with some dessicant is
probably the best bet, but it will take quite a long time. The
vacuum trick sounds like a good idea, but might give problems
with plastic insulation if you pump it down too far.

Best,
Chris.



--
Just remember, violence is the last refuge of the incompetent.
The rest of us don't wait until it's the only option. -- R B-W