This circuit can be used as an answering password system in a store, office, or other location. The circuit is from Intersil using components of the time. The circuit is from the 80's.
This circuit was found in a Popular Electronics from the 90s. Transistors are general purpose...
This circuit works with only 1.5 V and can be powered by a solar panel. The circuit is from 1991....
This circuit has a maximum output current of 5 A, and the 2N3055 must have an excellent heat sink....