[Hallicrafters] SX-42 Alignment

[Charlie]

I'll second that.....The SX-42 is almost as big a pain to work on  as 
changing out all those caps in the front end of an SP-600 !

73' Chas
----- Original Message ----- 
From: <roy.morgan at nist.gov>
To: "Rich Soennichsen" <rsoennichsen at gmail.om>
Cc: <hallicrafters at mailman.qth.net>
Sent: Saturday, February 17, 2007 5:03 PM
Subject: Re: [Hallicrafters] SX-42 Alignment


> 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
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