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 circuit was obtained in a 1978 publication. The SCR may be the TIC106. What it does is act as a...
In the figure we have a high input impedance stage with a general purpose PNP transistor. An NPN transistor...
We found this circuit in a Popular Electronics of the 90s. The circuit can be easily mounted...