This circuit was found in General Electric documentation from 1968. The circuit uses triac from the time as well as transistors that can be replaced by modern equivalents.
In the absence of a modulation signal, the carrier of this simple short-range transmitter is cut...
This circuit was obtained from an 80's Electronic Engineering. The circuit detects ice formation...
Other operational amplifiers series operatives, such as MC34072, MC34074, MC35071, MC35072,...