This circuit, which consists of an audio oscillator, was found in a Radio Electronics magazine from April 1966. The circuit is sensitive and is powered by a 9 V battery. The transformer is of a common type at the time.

This circuit, which consists of an audio oscillator, was found in a Radio Electronics magazine from April 1966. The circuit is sensitive and is powered by a 9 V battery. The transformer is of a common type at the time.