This circuit with two transistors was found in ancient European documentation. Transistors support equivalents. The indicator on this circuit is an ordinary 50 to 100 mA lamp.
This alarm, from a 1996 magazine, can be fitted with two BC548s in the original configuration...
This circuit is from a 1980s documentation featuring two time constants for sound decoding. The...
We found this circuit in a 1997 documentation. It uses a common analog indicator, measuring...