[Hallicrafters] SX-42 Alignment

[roy.morgan at nist.gov]

Quoting Rich Soennichsen <rsoennichsen at gmail.com>:

> Very frustrated trying to align this thing....

Yes, indeed.  Saint Peterr has a special list of folks who have tried to align
an SX-42.  They all get special arrangements upon arrival!

> ... Step two calls for
> setting the mode to CW, inject 455 KHz and adjusting A7 (transformer
> in BFO circuit for zero beat.  I get no beat at all. 

Be sue the BFO is working.  Test for negative DC on the oscillator grid (use a
VTVM with a high resistance in the probe to avoid swamping it out in case it IS
running).  Listen with a little probe wire on some other receiver, at 910 kc if
you can't cover 455 kc.  The crystal may be not working.  I think you can
dis-assemble it for careful cleaning.  If you have a 455 kc crystal known to
work, try paralleling it with the original, or substituting it.




> I performed the 10.7 Mc IF alignment, it went better except for the
> last step, I cannot find these peaks off the minimum.  May have to
> hook up the scope....

Do you have ANY kind of sweep generator?  If so, it's worth the trouble to set
it up.  The only successful allignments I've done or been party to were done
with a sweep setup.


> 
> On to the RF section.  Did not get far.  Hooked up the RMA dummy load
> and injected 1500 KHz into A1.  Adjusted A21 (RF cap) but I cannot
> find a maximum that corresponds to my injected signal. 

If you have not replaced any mica caps in the RF transformers, stand by to do
so.  They may well be shorted or shifted in value by this age.


 I find a
> maximum but it is not MY signal.  In fact it appears to be an actual
> broadcast signal.

You may have an oscillation.  a sensitive frequency counter with sniffer wire
may help.  Oscillations come from bad bypass caps (suspect ANY original cap
left in the radio), bad grounds (terminal strip ground pins, any tube socket
ground lugs, any ground lug under a nut, any if or rf can shields.)  The side
of the radio may need to be on and tight to get tough oscillations to stop.



> ... If I
> tune the radio to look for MY signal I find it at a dial indication of
> ~800KHz.

With your other receiver, make sure the local oscillator is running at near the
right frequency, AND that it responds as expected to changes in dial setting.
It can be that the LO section of the band switch is not on the shaft correctly.
If a PO (Previous Owner) had the shaft out, you must check each and every wafer
for correct orientation.



> The same sort of weirdness happens when I go to the next step and
> adjust A22 (RF coil).

Your RF sniffer/detector or scope with high impedance probe, coupled with a
signal generator can check tuned circuits for ballpark frequency.  A grid
dipper may be very hard to use due to the cramped (!) quarters that all those
coils live in.

> Frustrated, giving up for now.

Don't feel bad.  One of the most respected restorers I know gave up trying to
fix the next to highest band on one SX-42.  It's sensitivity was one thousand
times less than other bands.  We simply gave up.

Roy
K1LKY


Roy Morgan
13033 Downey Mill Road
Lovettsville VA 20180