This signal amplifier for ATV in the 427 to 439 MHz band was found in a magazine 73 for radio amateurs of the 90's. The circuit is installed next to the antenna on the mast itself.
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....