This circuit was found in the February 1971 issue of Radio Electronics magazine. It is designed to power the previous circuit, providing a maximum current of around 50 mA.
To obtain variable frequency signals, the circuit in the figure is recommended. In this circuit, the...
This circuit was found in old English documentation. It can be improved by using resistors of...
This circuit was published in a 1979 magazine, but it can still be easily assembled as the...