[Hallicrafters] Some HT-37 questions

[David C. Hallam]

Phil,

The power transformer in the HT-32/HT-37 have a propensity to fail.  A
simple resistance check will probably tell you if the transformer is
shorted.

You can improve the odds of your transformer not failing by using solid
state rectifiers and unsoldering the filament leads at the rectifier tube
sockets.  This keeps any high voltage off of the rectifier windings. You
will probably want to put some resistance in series in the low voltage solid
state rectifier to keep the LV from increasing too much or you can get a
Weber Copper Top SS replacement for the 5V4 that already had the series
resistance built in it.  It's not necessary to use series resistance with
the HV as the 6146's will handle the increased voltage without any problem.

There are people who will rewind your transformer if it is shorted, not
inexpensive, but certainly doable.

Watch out for stuck slugs in the RF coils.  I am fighting stuck slugs in the
20/15 meter mixer and driver coils in one that I am rebuilding.

All electrolytics probably should be replaced without bothering to test
them.  They are old and more than likely tired.  There are not very many
paper capacitors in the HT-37 and it wouldn't hurt to replace them too.

Good luck.

David C. Hallam
KC2JD

-----Original Message-----
From: hallicrafters-bounces at mailman.qth.net
[mailto:hallicrafters-bounces at mailman.qth.net]On Behalf Of Philip Atchley
Sent: Saturday, November 13, 2004 5:03 PM
To: hallicrafters at mailman.qth.net
Subject: [Hallicrafters] Some HT-37 questions

Hi Y'all,

I have acquired a Hallicrafters HT-37 HF transmitter that is very nice
physically, electrical status unknown.  This will probably be a "overhaul
project" later this winter (when I finish the SX-101A and the BC-1004
presently on the bench, they both belong to friends). But I've received some
Emails about the HT-37 that have me a little concerned.

Apparently they are known for power transformer failures.  Quote, "It's not
a matter of IF they'll fail, just when they'll fail".

Taking this into consideration, I have some questions as I deliberate the
upcoming task of overhaul (I'd hate to put a lot of work into it and find
the transformer is already shot).

1.  How can I determine if it's already failed?  Does it smell "smoked" or
show other indications (I know some failures can be invisible).

2.  Would it be safe to pull both rectifier tubes out and test it that way
for failure, checking for tube filaments, Voltage on the plate connections
of the rectifiers etc?

3.  Assuming the transformer is good, are there any things that I can do to
reduce/eliminate the chances of transformer failure.  Things like putting a
lamp in the case for a week or two to "cook it", solid state rectifiers,
fans, separate filament transformer to reduce load on the main transformer
etc?

4.  Are there any other "issues" with this rig?

5.  FINALLY, if the transformer IS already bad, and having a slim wallet,
would it be realistic to pursue fixing the transmitter up, or would I be
much better off "parting it out (It's really quite nice overall)?

73 de Phil,  KO6BB
http://users.mercednet.com/beaconeer/
Merced, Central California, 37.3N  120.48W  CM97sh

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