The oldest ancestor of the point-contact transistor was the crystal detector, used in early wireless sets.

ECONOMIST: The middle age of the transistor

By 1930, such vacuum-tube diodes had all but replaced the quirkier crystal detector.

ECONOMIST: The middle age of the transistor

But a few researchers, seeing the analogy between them, tried to put a grid into the crystal detector to turn it, too, into an amplifying triode.

ECONOMIST: The middle age of the transistor