Note
QST, Aug 1961, p. 2.
QST, Jun 1963, p. 161. (75S-3A)
QST, Mar 1964, p. 2. (75S-3B - "what's new?")
QST, Jan 1965, p. 140. (75S-3B)
Collins product catalog, 16M-CR-12-74
QST, Apr 1975, p. 2. (75S-3C - first reference in QST advertising)
QST, Feb 1977, p. 117. (75S-3C)
The successor to the 75S-1 added rejection tuning, a choice of crystal or variable BFO, and a 200 Hz CW filter. Other changes included concentric knobs for the RF and AF gain controls and selectable AVC.
The later 75S-3A version added extended frequency coverage with the addition of another 14-position crystal deck.
References
Frequency synthesizer for. Ham Radio, Dec 1975, p. 8.
Improved selectivity. Ham Radio, Jun 1976, p. 36.
Improved frequency readout. Ham Radio, Jun 1976, p. 53.
