We found this precision circuit in a manual from the 80's. The operational amplifier is of a common type at the time, and equivalents can be tested. Transistors are general purpose types.
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...