Found in an American documentation from the 90's, this circuit aims to light a neon lamp with voltages from 5 to 15 V. It is a small inverter that operates close to 15 kHz.
This 1967 Raytheon circuit uses an optical coupler of the era and has a range of 800 to 200 Hz....
This interesting digital counter with relays with complementary outputs was found in the Radio...
This circuit uses a diode as a radiation sensor. The operational ones are old because the...