Found in an American publication of 1968, this circuit makes use of a pilot light of the time. It can be replaced with LED with appropriate series resistor. Transistors may be modern equivalents.
Suggested by Texas Instruments in 1980s documentation, this circuit uses a component of the era....
The idea of this simple circuit is to use a tape recorder to key a transmitter in code emission....
This relay circuit with a dual channel MOSFET (not very common today) was found in an old American...