This circuit is from a 1980s Motorola documentation. The circuit can be made with modern equivalent components. The original circuit is for the 115 Vac (110 V) grid and has two settings.
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....