[Hallicrafters] A cautionary tale of my SX-42

[Craig Roberts]

I am happy to report that my SX-42 now functions perfectly in all 
respects. The last remaining problems -- no BFO on  the 10.7 MHz IF 
bands and no FM metering -- were solved last night with the reheating of 
a single solder joint.  The cold solder joint was mine -- the second one 
I introduced during the rebuild.

I must explain that I solder meticulously.  I got plenty of practice as 
one of the "Hams at Heath" years ago who assembled demo and early 
production units.  But soldering new components to new terminals and 
junctions is one thing. Soldering old bits is another.  Whenever 
possible, I remove an old component completely with the use of 
desoldering braid. (a vacuum driven desolding station would be nice, but 
they cost as much as a nice old radio), then install the new component 
with as firm a mechanical connection as possible, apply appropriate heat 
to the junction and feed in just enough solder to secure the 
connection.  In well over 99-percent of the cases, this works 
perfectly.  However, old terminals are often heavily oxidized and may be 
saturated with ancient flux residue and dirt.  Every so often, the 
reheating of such a terminal dislodges this non-conductive gunk just 
enough to spoil the new joint. While your new mechanical connection 
might be good, the old connections to other components may not be. (Some 
manufacturers were more careful about good workmanship than others). So, 
this boiled gunk may migrate under an old component-to-terminal joint 
and compromise the connection. 

That's why it's important to examine each resoldered joint very 
carefully and, for that matter, not be afraid to "correct" the old 
workmanship by cleaning and re-wrapping a lead.  And don't be tempted to 
repair old, questionable joints by simply heating and dumping more 
solder on them. Suck the old solder off and apply fresh. You'll find -- 
in certain radios -- that many factory connections have much more solder 
on them than is necessary. Applying even more is sloppy at best and can 
do more harm than good at worst.

Of course, not all malfunctions can be traced to the manufacturer.  Last 
week, as my SX-42 rebuild entered its final stages, I removed a couple 
of tubes to do some chassis cleaning -- at 2 o'clock in the morning (you 
know how that goes).  In a sleepy haze, I swapped the tubes while 
replacing them. One was the voltage regulator.  Upon powering up, a 
sizzling sound and small curl of smoke jolted me fully awake as one of 
my brand new power supply filter caps self-destructed.  True and 
luckily, the repair took just a few minutes, but it was a careless and 
wasteful episode.  As I've reminded myself before, don't work on old 
radios -- or old tractors, locomotives or power substations -- when 
you're tired or feeling poorly.  The side effects can range from 
embarrassing minor inconvenience to death or, worse yet, getting sniped 
at by the XYL. "I told you to go to bed, but would you listen?....."

73,

Craig
W3CRR