These receivers pictured side by side are an interesting comparison. The 75S-3A is a "some what" rare unit. The value being about twice (08/00) that of the 75S-3 (Note: the
75S-3C is about five times the value of the 75S-3 in the collectors market 08/00). The 75S-3's came standard with a 200Hz. CW filter (soldiered in). With the 75S-3B, Collins added the "FA" style multiple plug in
filters (one standard -- 2.1KHZ SSB filter -- others sold as options). The High Mu filter cover added by Dennis Brothers when he restored this receiver to better than factory specifications has been removed to allow a view of the filters.