This analog ammeter circuit was found in documentation from the 1980s. The components admit equivalents and the scales are determined by the values of the components in the range selection.
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...