Found in a 1967 EEE, this circuit generates a constant amplitude signal, stabilized by a zener diode. The circuit can operate with voltages from 18 to 22 V.
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....