Two Wireless Detectors
     A month or two after I made my presentation to the New Jersey Antique Radio Club on mounting mineral crystals for detectors, Marv Beeferman ask if I’d examine two detectors that he had obtained in a box lot at the Henry Ford Museum auction last year.  He handed me two brass cylinders about an inch and a half in diameter.  Each had a hard rubber base with two brass pins. 
     When Marv first obtained these devices, the brass covers were tightly jammed on the bases, making it impossible to identify their function.  I’m sure if any half-way-knowledgeable radio historian had seen the insides, they would not have been in a box of effluvia.  When Marv carefully opened the cases, he found  two marviously constructed crystal detectors, neither of which involved the usual galena and catswhisker.
    The first detector contained a small piece of rock, showing the unmistakable red-orange color of zincite (zinc oxide), in contact with a second mineral sample.  This is the classic perikon detector.  The second mineral is probably Bornite, Cu5FeS4, but it’s hard to make a positive identification without damaging the specimen.  By the way, zincite is a rare mineral except in the Franklin area of Northern New Jersey. (Local interest.) 
    The second detector consisted of a piece of layered lead-grey material, held in a carefully machined clamp, in contact with a hairpin-shaped flat metallic spring.  After consulting several vintage radio books andA Field Guide to Rocks and Minerals by Frederick H. Pough, I identified the mineral as Molybdenite, MoS2, an early favorite of the Telefunken Company. 
     I carefully cleaned the contact surfaces of both detectors with isopropyl alcohol and tried them in my laboratory reference crystal set.
     The perikon detector showed a very weak signal from local powerhouse WOR.  Tightening down on the thumb screw improved things.  Tightening some more, resulted in still louder reception.  All in all, its performance was about what I had expected from my reading: ok, but not nearly as sensitive as Galena or a modern germanium diode.  As a rough comparison, I’d say it works about as well as a silicon diode.
     The “moly” detector just barely worked, despite repeated adjustment of the contact. The application of a little DC bias to the detector, provided by a potentiometer across a pen-light battery, brought the ancient semiconductor to life.  Performance was about on par with the perikon unit.
     Detectors of these kinds were used in commercial applications because of their ruggedness.  A galena detector requires a very delicate touch from the catswhisker, making it a poor choice for use on a vibrating ship in rough waters.  Also the rectifying junction of a galena detector can be easily destroyed by a distant lightening strike or RF from the transmitter.
     Because of the materials and construction style employed, I’m guessing these detectors were built during the wireless era for commercial or experimental application.  They were probably made in the United States, as the screw threads are standard SAE types.
     If any of our readers have further information on these units, Marv and I would like to hear from you.

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