[Hallicrafters] HT-37 saga

[Al Parker]

Hi folks,
    I thought maybe my experiences of last week would be of some interest.
    I got an HT-37 abt 2 yrs ago to compare with my HT-32, performance &
audio quality wise, etc.  Shortly after I got it cleaned up, aligned, etc,
the pwr xfmr did the common thing, HV winding to fil to gnd.  So, I put a
Heath HP-23 on the end of an umbilical cord.  It worked real slick.  After
doing it I discovered I'm not the first to do it.  I made it easily
reversible, just in case I came upon a good xfmr, or sold it to someone who
doesn't like mods.  Well, the good xfmr arrived last week, and in
it went.  The following is an account of it from there on, sent to a few
friends---
    Wed.PM I said:
"Just abt to
finish up SS'ing the HT-37 p.s. after replacing the pwr xfmr, per Lynn's
recommendation.  The xfmr I got looks practically new, I put a 60w bulb
under it overnite & then also left it at abt 50vac for a few hrs without
rectifiers, so hopefully I've driven any moisture out & it'll live a long
time without the 2 5v fil. leads hooked to anything."

then, Thurs. noon:
"    I had mentioned in my msg that I was abt to fire up the HT-37 w/new
xfmr, which I had really babied.  Well, I tried.  It produced HV & LV at
half AC input, but when I turned it up to abt 80v it blew the fuse.  To
make a story shorter, it appears to have a short in the primary, it's abt
0.7 ohms, I'd expect several ohms.  No indication on the 20meg scale of
anything to gnd or any other winding.  It draws 3-4 amps at <20vac in, I
finally rigged up an ammeter with the variac.  I was disconnecting leads a
bit ago when the xyl came home with the groceries, so I did the unloading
bit, will get bk to the xfmr after lunch.  Maybe it'll be repairable,
hope-hope."

Then Thurs late PM:
"Hi Guys,
    Well, don't jump to conclusions is the lesson learned.  Xfmr OK, but
took a while & effort to decide so.  I ckd & re-ckd it & the p.s. ckt, etc,
b4 removing it.  All looked OK, but still expected the primary was the
trouble.  Turned out one of the diodes in the HV ckt went out.  I had 2 in
series for each leg, the other one didn't go so all the ckg didn't show it
shorted.  Don't know why the other 1 in the leg didn't short.  I didn't
figure it out until after I had removed the xfmr, pulled it's bells off &
looked.  Ckd with a megger.  No windings showed anything between others or
gnd.  Then hooked it up to the variac.  Didn't pull any pri. current, HV
came up OK, etc.  Put 3 diodes in series just to be sure, and put it all
back together again.  Seems like I do things twice on a lotta stuff.
    Now I just gotta find out why nothing else happens after the relay
clicks in.  Got this far b4  supper, then went to radio club mtg tonite.
Maybe tmw.
    At least I'm relieved it's not the xfmr, just a 10 cent diode, even if
I shoulda figured it out b4 doing 2 hrs work."

    Fri. PM it all came together.  The problem was a dirty bandswitch & the
bias voltage needed to be reset after the new p.s. work.  Put it on the
air, made a few QSO's.  100+w on all bands.
I'm happy now, 73,
Al, W8UT
New Bern, NC
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