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4 × 3.2 × 1.2 cm

Galena (Lead Sulphide) was the crystal of choice in crystal sets of the 1920s. It was used as a detector in connection with a catswhisker (a piece of brass or copper wire with a sharp point).

The combination was the equivalent of a Schottky diode. However it also typically included a number of actual Galena crystals. Thus there were a number of included grain boundaries. The diode operation was therefore a little more complicated than for a single crystal.

A kit could be purchased, which had Galena crystals laid on cotton wool, in a small tin similar to those used to hold gramophone needles. A pair of tweezers for handling the crystals was included in the kit.

It was recommened that the crystals not be touched with bare hands, and that the crystal be embedded in a low melting point metal (eg Woods Metal) to hold it rigid and maintain good contact with the crystal holder.