This 1967 Raytheon circuit uses a Raystor, an optical coupler with a lamp and an LDR. The circuit can be adapted to use another type of coupler.
We found this circuit in the Texas Instruments' Linear Circuits Applications. It uses an...
With the circuit in the figure, it is possible to control the amount of heat generated by the...
This VHF receiver with three transistors and loudspeaker listening was found in European...