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.
We found this circuit in a 1964 Electronic Design. It divides the frequency of a 20 MHz signal by...
This circuit was found in the November 1987 Radio Electronics magazine. The trigger voltage is...
This high-powered megaphone circuit is from a Radio Electronics from December 1964. Note the use...