[Hallicrafters] HT-37 restoration

[Mark Shaum]

Art's spam filter nailed me, so I'm replying to the list.

----- Original Message -----
From: "Art Lebermann" <artleb at earthlink.net>


> I'm about to start restoration of a HT-37, which seems to be in
reasonably
> good shape (no missing parts - as far as I can tell).  Any thing I
should
> watch for?

Art,

Just got my HT-37 off the shelf here a week ago, dusted it off after a
couple years of unuse, and have had it on the air several times on CW,
AM and SSB paired with my recently repaired SX-111.   A few things come
to mind, none terribly important, but you might:

1 - Replace the selenium bias rectifier SR1 with a silicon rectifier.
You may need to increase the resistance in series with the rectifier to
compensate for the lesser voltage drop of the silicon device (i.e.
increase value of R63).  If you plan to use the unit often, the original
selenium stack rectifier will fail, eventually.  If you have never had
this happen, let me say the penetrating odor that results is much worse
than any industrial strength skunk could spray around your radio room.

2- Install a current limiter in series with the power transformer
primary.  I have one rated at 5A from Mouser in my HT37 as well as in my
32B.  With the function switch sequence of power off - stby - mox there
is a tendancy to turn the knob too far counterclockwise as you return to
standby, accidentally powering the unit off.  Instinct then makes you
immediately twist to the right and power the rig back on, often with a
big "thwang" as the ac surge hits the transformer during the peak of an
ac cycle.  Several power tranformers have been lost due to this over the
years, Hallicrafters even sent a service note out on the topic.

3- Solid stating the lv and hv b+ supplies - optional in my opinion, but
if you do, you may as well remove and tape off the existing filament
rectifier leads.  One less path for the hv ac to short to within the
transformer.

4 - If you plan to use the set on AM, do not set the output carrier
level per the manual.   Use the shack wattmeter and set it for no more
than 20 or 25 watts unmodulated carrier.  Apply enough AF gain just to
hit 100% modulation on voice peaks.  Just like with a modern 100W solid
state rig.

5 - You must keep the SWR down below 2:1 or so.  The PA has no
adjustable loading, so expects to see a near 50 ohm load for proper
operation.

6 - There is no ALC in the transmitter.  Overdrive by cranking the mic
gain too high and you will irritate everybody within many khz.

7 - Sideband suppression is somewhat limited.  The best I can manage is
about 30-35 db across the entire audio range. This is fine for general
purpose
use, but filter rigs do better.

Keep the wafer switches and pots cleaned and lubed, and the old set
should go on for a good long time.  You will receive many excellent
quality audio reports on SSB and AM.  I prefer the D-104 mike with
this set.

73! - Mark K9TR