This circuit is from an American 80's documentation. The circuit indicates when the voltage of a 9 V battery drops below 7 V. The transistors can be BC548.
The circuits shown by figure below are simple stages using JFETs. The gain are 25 and 150...
This circuit was found in the November 1989 Radio Electronics magazine. Power supply depends on...
This circuit was found in an old publicatio n from the year 1958. The circuit controls an external load by...