The starter circuit shown in the figure was found in an old European documentation. The circuit makes use of an SCR which is still common and the diac can be of any type.
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...