This circuit was obtained in a Electronics World of 1968. The transistors can be equivalent as the BC558 for the PNP and the BD135 for the NPN powering lamps from 3 to 12 V according to the supply.
This circuit is from a Harris Semiconductor datasheet from the 80s. However the circuit can be...
Described in an article that taught how to assemble the complete intercom in Radio Electronics magazine...
This circuit indicates when the voltage of a 12 V battery is low. With changes, for example, the...