This circuit was found in an English publication from the 70s, an article that teaches how to calculate instruments. The circuit is still current and can be built with an analog indicator of 100 uA.
This source was found in American documentation from the 60's. The diodes are germanium, and the...
Found in a May 1968 Supertena newsletter in Popular Electronics magazine, this mid-waveband...
This circuit can be used in alarms by activating a relay or a current load that depends on the...