This circuit was found in the March 1997 Electronics Now magazine. It uses a common analog indicator and the transistor is a general purpose one.
B In this circuit we show how to use an electret microphone powered by a small battery (can be of...
This circuit is from a 1976l filter cookbook. The circuit has a factor Q = 3, and must be supplied...
Using transistors at the time, this circuit was found in a 1970s documentation. Transistors support...