This receiver circuit was found in a Hands On Electronics from the 90s. The circuit uses a PLL 561B that is not a common component today.
We found this transmitter in 1980s documentation. Coil data is found next to the diagram and...
The circuit shown here produces a pure square tone of 440 Hz that is suitable for musical...
This circuit, which may have more inputs, consists of an optical OR gate using common...