Tune (tuning) indicator: a lamp is connected to one end of a loop of wire and a adjustable tap. The loop is placed in series with the earth lead of the jigger secondary coil, and the tap is adjusted to give a reasonable brightness at maximum antenna current. Other positions might lead to bulb burn-out or the lamp being too dim to observe the light.

The lamp indicates by its brightness the current in the aerial circuit, which is adjusted for a maximum by varying the tuning inductor (jigger or spiral inductor).

Tune indicator ST 021416 achieves the same result as ST 21422 but in a different way.

Physical Description

Varnished wooden board with an approximately 270 degree arc of wire connected to two terminals. A wiper arm, fitted with a knob, is connected one side of a lamp socket; the other side is connected to one end of the loop. The globe is missing.

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