Found in an Electronics World of 1966, this circuit makes use of FETs of the time. Modern equivalents can be used. The high voltage supply suggests its use with tube amplifiers.
This circuit with 5 V power was suggested by Motorola's Linear Databook of 1990. The circuit has...
We found this circuit in a 1982 documentation. An intercom to be good must be sensitive and have...
This circuit is indicated to determine the flight time of an electric motor model airplane. The...