This circuit was found in the September 1972 issue of Radio Electronics magazine. The circuit uses an operational amplifier of the time and a symmetrical 9 V source.
Any general purpose PNP transistor such as the BC558 can be used on this circuit from an old...
This circuit is from a 1965 General Electric hobby manual. The circuit can be assembled with...
This circuit was found in a Maxim documentation from the 90s. It is valid for the lower income types...