[Hallicrafters] SX115 Mode switch problem on LSG

[lardiere at ix.netcom.com]

All,

Yep, just found a similar problem in one of my two SX-115.  The LSB died.  I replaced the crystal with one from the other receiver - fired right up.  Tweaked T8 slightly to balance the gain with USB.  

I now remember that I had already replaced the USB crystal in the other receiver, too.  So the crystals are, indeed, failing after a number of years of operation.

Why does a crystal fail?  Most likely poor contact between the internal contacts and the crystal itself.  Could be oxidation after many, many years.  Or perhaps the temperature cycling being next to a tube tends to microscopically fracture or disturb the internal contact points.  I am sure there are crystal experts out there who are familiar with this sort of thing.  These SX-115 crystals must have had a production problem to be failing at these rates.  Or it's the proximity to the tube.  Or both.    

Anyway, the fix is easy - buy another crystal and check the crystal activity alignment per the manual.

73,

Rocco N6KN

. . . 
>
>Ive had several radios with crystal problems in the past year or so, all in 
>the roughly 1955-65 build era. A 51J4 is the latest; no more Band 1.
>
>I wonder what the failure mode is?
>
>Carl
>KM1H
>
>. . . 
>
>> Mike,
>> I had the same problem with my SX-115 and I've had a similar problem with 
>> a Hammarlund HQ-215.  (Hmm, last two digits the same; maybe it's a 
>> numerology problem.....) I ended up replacing the BFO crystals in both to 
>> get reliable operation.  But try the alignment of the coil first, and 
>> replace any old paper capacitors.
>>
>> Bob K4ERR
>>
>> Mike Anderson wrote:
>>> Maybe someone has run across this problem. I have a SX115 in excecellent
>>> condition, when a rotate the mode switch to
>>> LSB/CW or LSB/SSB I have a noiseless audio. If I rotate the mode switch
>>> to USB/CW or USB/SSB we have results, the receiver acts like a 75A4 in
>>> performance. What should I do to troubleshoot this rig give the
>>> operation issues. Has any one run into this problem before.
>>>
>>> Mike Anderson
>>>
>>> N5MV
>>>