This carbon microphone circuit was found in a Radio Craft in May 1947. The circuit replaces the battery that is normally used to bias the microphone and functions as a preamplifier. Power comes from the mains without isolation.

This carbon microphone circuit was found in a Radio Craft in May 1947. The circuit replaces the battery that is normally used to bias the microphone and functions as a preamplifier. Power comes from the mains without isolation.