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.
Found in documentation from the 90's, this circuit has a narrow pass band around 1 kHz. The...
This circuit was found in a Radio Electronics magazine from November 1991. The circuit operates at 2.2...
Found in old documentation, this circuit has only the most difficult component to obtain the PUT....