This circuit was obtained in a 1964 Electronic Design. Equivalent modern transistors can be used. The circuit requires a 6 V symmetrical power supply.
This intercom uses transistors from the 60s. It was found in a Japanese publication at the time....
Found in a Hands On Electronics from the 80's, this circuit activates a relay with alternating...
This circuit is from an American magazine Popular Electronics of March 1991. The circuit produces both...