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.
This circuit was found in an American documentation from 1969. Indications of the used transistors are...
We found this circuit in a 1960 Sylvania transistor manual. The relay can be 12 V and C1...
This circuit was found on an 80's Ham Radio. The transistor admits equivalent. The circuit can...