CRYSTAL SET

Pictured is a catswhisker crystal set of 1940 vintage. It may be a kitset as it has no brand name, and the coil inside has packing in the form of some old newspaper. The newspaper is dated 14 March 1944. The set consists of a wooden box, typical of the time, with the coil inside, and the catswhisker on the top bakelite cover with the brass terminals. The catswhisker detector consists of a piece of galena (lead sulphide) in a holder and a moveable arm with a thin wire (catswhisker) on one end. The position where the wire touches the galena, forms a point contact diode, and acts as the rectifier. The internal coil has a slider which is used to adjust the tap on the winding, and with the catswhisker, enables a station to be tuned in. The high impedance headphones are connected to two terminals, and an aerial and earth are connected to the other terminals. This set was found in a Port Adelaide antique shop. The headphones were open circuit, 2 terminals were missing, the catswhisker arm was gone, the slider was tangled in the coil windings, and several wires were missing. A new catswhisker arm was turned up on a lathe from brass, and 2 new screw terminals were also made. The set works very well for its extremely simple design. I disconnected the catswhisker and substituted a germanium diode as a test. The performance was better but not a great amount. I measured the resistance of the germanium diode verses the catswhisker, and found the forward resistance was similar, but the reverse resistance was quite low, compared to the germanium diode.

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