This circuit was found in General Electric documentation from the 1980s. The circuit is intended to receive 50 kHz modulated optical signals. The components support modern equivalents.
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...