This circuit, which can be used as a shield, was found in a 90s Electronic Design. The circuit uses a diac and the transistor can be general-purpose.
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....