This simple injector and signal follower employs a high impedance headset. Transistors can be of general use. The circuit is from old American documentation.
This circuit uses a small photocell to trigger an auxiliary flash. The circuit is from a 1991 PE...
This circuit is from a Popular Electronics from July 1990. The magazine no longer exists, but the...
This telephone circuit was found on a 90's EDN. It keeps a flashing LED to indicate that there was a...