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.
I found this circuit in a July 1982 English magazine. The circuit is still viable by simply using...
This simple general-purpose circuit was found in a 1987 publication. It is a simple preamplifier powered...
This configuration has already been found in other manuals, as the LM117 is manufactured by...