SB-401 CW Chirp problem

[Mark V. Johnson]

Wondering if anyone has had problems with "Chirp" reports using  an
SB-401/SB-301 combo. I've gotten them  (chirp reports) on 20 and 15
meters lately and I have it narrowed down to the  Het Osc in the SB-301.

When I listen to my signal  on another receiver while transmitting into
a dummy load, I can hear the frequency shift enough to be "chirpy". When
I transmit using only the SB-401 in stand alone (I have the optional
Xtal pac) the chirp goes away.

I did find that the SB-301 Het OSc adjustment has an effect. It seems
that if you have the Het Osc adjustment too high, it  causes the
chirp...Must be over driving the  transmitter. Yet, the manuals
(SB-301/401) have you adjust the Het Osc coils in the SB-301 for maximum
grid drive in transmit on teh SB-401. When I back them off and adjust to
the spec's listed in the receiver (less than -3VDC at the  Het Osc test
point), the chirp goes away, yet the Sb-401 grid drive is not at maximum.

Seems these combo's (sb-301/401) are very adjustment sensitive....

The Het Osc circuit in the SB-301 seems to be OK...Tube (6AB4)  is new
and has good gain, voltages are to spec....The 6AW8 Het Osc amp in the
SB-401 is good...Voltages are fine.......I'm using RG-62 cut to the
proper length.....When I scope the Het Osc signal, it looks
fine....Symmetrical Sine Wave...No crap...


Anyone have similiar expereince??? Many Thanks!!

MV Johnson VE3DJU/VE3DDI

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