Journal Archive

Platinum Metals Rev., 1961, 5, (3), 95

Iridium-Platinum Wire for Diodes

The point contact diode is still widely used - particularly in domestic radio and television receivers - because it is cheaper to manufacture than the newer junction types. It is a development of the “cat’s whisker” detector used in the early days of broadcasting and consists of a small dice of single crystal germanium with a fine wire or “whisker” in contact with it.

Tungsten is widely used as this material, but the metal forms a stubborn oxide film on the surface. In order to overcome this, and so achieve the required performance of the device, the General Electric Company Limited decided to use 20 per cent iridium-platinum wire for their type GEX 34 diode.

This alloy, which is used in the form of wire .004 inch in diameter, is hard enough to give the required pressure at the point of contact. In comparison with tungsten it is easier to form and the cutting and crimping tools require less maintenance. Moreover, unlike tungsten, the alloy is completely free from tarnish films.

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