Boston based recordist, engineer, music critic, and generally interesting person Micha Schattner (WGBH, WBUR, BAS, NPR and many others) stopped by the lab with his ultra rare Cambridge Microphone ribbon mics which he uses quite often. Cambridge Microphone was created by inventor Charles P Fisher in the late 1960's and his innovations, which include the tapered pole piece arrangement and tapered adjustable ribbon, resulted in US Patent 3,435,143. These were built in the mid 70's and used a +48VDC supply.
By the way, where the heck is Charles P Fisher? Anybody know?It is quite unusual in design, and has a transformer coupled amplifier/emitter follower powered by a split 15V external supply. All of the electronics except the supply are in the body of the mic.
The mic in the picture has a stretched ribbon, which is common in all aluminum ribbon microphones. We're going to replace this ribbon, make some measurements, and get the mic back in service this week.