Found in the February 1983 Radio Electronics magazine, this circuit uses a FET and has good gain at the frequencies determined by the components. The FET is any general-purpose FET.
This circuit appears elsewhere on this site, but from different sources. Using the LM3900, we find this...
This interesting source or isolation transformer also allows to vary the output voltage by...
In this circuit the CA3140, an operational amplifier, is used as a comparator with the zener diode...