[Hallicrafters] SX-100 BFO Setting

[Rodney Bunt]

Inject 50kHz into the IF and adjust for ZERO beat. inject at pin 1 of V6.

NOTE: the IF freq depends upon which version of XS-100 you have. The IF for a SX-100Mk2 is
50.75kHz, for a SX-100Hk1 it is 50.5kHz

A real seat of the pants adjustment is to set selectivity to 500Hz (.5kHz) remove antenna and tune
the BFO for the lowest pitch noise, it will go down and back up again, adjust the 'whoosh' for
lowest pitch.  

Rodney
VK2KTZ

--- Frederick Bray <fbray at mminternet.com> wrote:
> I am finishing up the restoration of my SX-100, but I have had problems
> adjusting the BFO as described in the manual.  It is probably my own
> fault that I lost the original adjustment.  When I got the radio, I
> couldn't the BFO to function, even after re-capping the radio and
> replacing the tube.  I assumed that the former owner had mis-adjusted
> the coil tuning and tried adjusting it throughout its range to no
> avail.  Turned out that one of the resistors in the circuit had
> increased in value well up into the megohm range, dropping the voltage
> below what was required.
> 
> Anyway, after replacing the resistor, the BFO works, but I can't get it
> adjusted down to the spec's in the manual.  I figure that I could
> probably set it correctly using my HP freq. counter -- which goes down
> to 10 Hz. or with a scope.  Unfortunately, I can't find the right point
> and/or technique to pick up the BFO signal without loading the circuit
> to the point that I substantially change the frequency.
> 
> I wonder if anyone has been down this road and can offer suggestions as
> to where I might pick off the BFO output so that I can set it to 50 KHz?
> 
> Many thanks.
> 
> Fred
> KE6CD
> 
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> dfischer at usol.com
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