[Hallicrafters] S 38-D Oscillation

[Roger D Johnson]

Brent Seres wrote:
> Hi Folks
> 
> I'm looking for some help retoring an S-38 D. I have re-capped the unit 
> and performed the alignment as per the service manual. The radio seems 
> to be working well except for 2 minor problems:
> 
> 1) On weak signals (especially on the BCB, below about 1200 kHz), there 
> is an oscillation, much like a weak BFO signal that goes to zero beat as 
> I tune through the station The BFO is off, the IF is aligned, and poking 
> and prodding at components does not seem to have a significant effect, 
> such as changing changing the amplitude or frequency of the note.

Hi Brent...

This is often caused by harmonics of the local oscillator
beating with a strong short wave station. The S-38 series
doesn't have much selectivity ahead of the mixer and will
be prone to this problem. If this is the problem, the beat
note will "tune" faster than normal. As an example, if the
oscillator 2nd harmonic is beating with a station, the beat
note will tune at twice the "normal" rate.

73, Roger
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