This circuit was found in Sgnetics documentation from the 80's. The circuit also has loudness control. The power supply must be symmetrical.
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...