This circuit from a Popular Electronics from the 90's can generate signals from 0.03 Hz to 3 kHz depending on the value of the capacitor and resistor.
This photoelectric cell light relay was found in Radio Electronics magazine from April 1958. The...
The circuit shown in the figure serves as a pre-amplifier with a voltage gain of around 12 times,...
This circuit uses a lower frequency crystal in an excitation system for an oscillator with a coil...