This circuit is from a Radio Electronics from October 1963. The transistor is a power transistor of the time, and two transformers are used. The input has 10k impedance and is powered by 12 V.
This is the battery-powered version of the previous circuit. The circuit is from the same Radio...
This is the modern version of the Galena radio in which the detector is a germanium diode (which can...
This circuit triggers a remote doorbell when the phone rings. The circuit is for the 110 V mains...