This sensitive 4-tube, battery-powered receiver was found in a 1949 Radio Electronics. The circuitry was wired in crystal earphones.
This circuit uses high voltage transistors to provide direct power from the 110 V power grid or a...
This circuit was designed to work with the previous one in triggering a relay by the sounds picked up...
This circuit was suggested by Signetics in 1980s documentation. The circuit makes use of the...