Found in an American publication from 1968, this circuit can be made based on a TIP42 that must be mounted on a heat sink. The transformer is 25 V with a current of 3 to 4 A.
This fast trigger circuit allows the counting of up to 300 pulses per minute. The circuit is from...
This intercom uses transistors from the 60s. It was found in a Japanese publication at the time....
This circuit is from an old publication from the 90s, but it can be adapted to operate with LEDs....