[Collins] 75S-1

[Dr. Gerald N. Johnson, electrical engineer]

Looking at my old 75S-1 schematic (Collins yellow SSB book), I see it
has only a single AGC time constant capacitor, not the dual time
constant (fast attack, slow decay) of the later receivers and without
selectable time constant. Often it sounds even better if the RF gain is
backed off (which injects a negative bias into the AGC circuit) so the
incoming SSB or CW signal just barely raises the meter above the RF gain
setting. Just tickles the meter. That way the receiver gain doesn't rise
during pauses in the signal and you get a better overall signal to noise
ratio.

If it has black beauty capacitors, they may be contributing AGC circuit
leakage to shorten the time constant further.

PTO linearity probably depended on the time of the week when it was
assembled. There's much hand work in adjusting the linearity. And its
entirely possible that lumpy dried grease on the lead screw is
contributing to less than perfect linearity.

73, Jerry, K0CQ, Technical Advisor to the CRA
-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.