This circuit was found in a 1968 Hughes documentation. The transistors are from that time. The coil is for the medium or short-wave range.
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...