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.
The circuit shown in the figure can be used as an indicator of presence and high voltage in a...
This circuit uses the 2N626, the first commercial Darlington transistor. We found it in Radio...
This circuit can generate signals from 80 to 800 Hz with an amplitude of 0.3 V. We find it in a...