This circuit was found in a 73 magazine for radio amateurs from the 90s. The circuit uses high voltage transistors and the relay is high voltage as well.
This FM advertising suppressor (SCA) decoder circuit was suggested by Signetics in a 1980s...
We found this circuit in an old General Electric documentation. In fact, PUTs are not common...
We find this simple musical instrument in a 1977 Radio Shack documentation. The key resistors must be...