This circuit with germanium transistors is from 1960 and was found in Mullard's transistor application manual from 1960. The circuit can be adapted to use more modern transistors.
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...