This circuit was found in documentation from the 1980s. It is powered by the audio signal that must be cut. Transformers are the critical components and transistors are 2N2222.
This Texas Instruments circuit uses a phototransistor to fire a TTL trigger port. Other...
This simple SCR delay circuit for activating a relay was found in documentation from the 1980s. The...
We found this circuit in Japanese documentation from the 1960s. Transistors are types of the time...