One reason why simple transistor radio circuits proved challenging for early transistor experimenters was the low input impedance of bipolar junction transistors. This made it difficult to come up with an efficient circuit for a one-transistor radio.

But by 1966, the problem was largely solved by the appearance of the field effect transistor (FET), whose electrical characteristics were essentially identical to those of a triode vacuum tube. Fifty years ago this month, the September 1966 issue of Electronics Illustrated carried the plans for this one transistor regenerative receiver for the broadcast band.

The circuit used a Texas Instruments 2N3820, which sold for $3.75 plus shipping, and put out good headphone volume with a single transistor.

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