Based on an LM36000 OTA this circuit was found in the July 1988 issue of Radio Electronics magazine. It covers frequencies in the range of 45 Hz to 45 kHz.
This typical crystal oscillator configuration can generate signals up to a few tens of megahertz...
This simple servo can be built by coupling a potentiometer to a reduction box with a 3 to 6V...
This constant current source for high voltage loads was obtained from a 1967 General Electric...