[Hallicrafters] re: SX-42 Hum(bug)

[Al Parker]

Hi Mike and all,
    I have 2 SX-42's, One I've only done some cleanup on, the other has been
nearly completed, and is in operation & getting it's final tweaking, etc.
(been in that process, off & on, for abt 3 mo.s)  I'm late on this thread,
but here goes --
    As somebody said, take a look at the several websites that have SX-42
work shown.  Do not use the rcvr until you have replaced the several caps
that have been ID'd as killers to output xfmr or bandswitch.  (I don't
remember them offhand, but find them).  Use the schematic to ID every
component you work on, don't just replace caps or resistors without
understanding where they are in the circuit, it's a great learning
experience.  If you can, do a section at a time & then power up & listen,
it's easier to find any mistakes that way ;-)
    I didn't see anyone mention one thing to make it easier to work in
there - remove the left side panel, by the RF section.  That makes a real
miserable job just a tough one.  Some of the paper caps in the RF secn are
almost impossible to remove, you may have to split them & take out in
pieces.  And don't feel bad about just cutting the lead off at the switch
terminal & soldering the new lead onto it, it'll reduce the mechanical &
heat stress of removal on the switch.  Use a low wattage soldering iron,
near the switch sections in particular.
    You will have to replace all the brown, waxy, paper caps.  All that I've
removed from an SX-42 or SX-28 have been leaky, usually when only tested
with an ohmmeter.  I removed 2 recently that I had missed earlier, one
showed bad at 25v on the tester, the other went to abt 150v.  I think actual
capacitance on each was way off.  Check resistor values, particularly in the
plate, screen & cathode ckts.
    my s/n HA68803, P.O.#1046, (the one I've been working on) has
non-striped Black Beauties in it.  I have not replaced them in a wholesale
manner.  Every one that I've tested has been good, capacitance & leakage (up
to 450v).  I have replaced all the hard to get to ones, particularly in the
RF section.  It's pwr xfmr toasted last Winter, it now has a Gary Brown
rewind job, he did a beautiful job.  (we consulted and he increased primary
windings to reduce secondary voltage, as my line voltage is close to 125.)
    s/n HA74270, also P.O.#1046, has striped Black Beauties in it.  They
don't look quite like the notorious BBOD's of SP-600 fame, but close.  I
haven't ckd these at all yet, have never powered it up at all, will wait
until I get into it.  I'm not confident that they'll be as good as the
other's.  On an SP-600 you must replace them all.
    Both of these have repainted & screened front panels, and repainted
cabinets, I expect they'll be real pretty when done, and am planning to have
them in top electrical condx.  One's a keeper, one has a tentative new home.
    Have fun, "if it ain't fun, don't do it"
73,
Al, W8UT
New Bern, NC
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