Found in a Maxim publication from the 90s, this circuit generates signals from 10 to 25 kHz with a THD better than -80 dB. The circuit makes use components of the time.
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...