This battery-powered 3-valve circuit was found in American documentation from 1947; Two batteries are used, one high voltage and one low voltage for the filaments.
The sensor is S1 in this alarm that we found in a Radio Electronics magazine from May 1971....
This circuit was found in documentation for radio amateurs of the 1980s. This is the so-called...
We found this circuit in an American documentation from the 90's. The circuit makes use of general...