This circuit was found in an American publication in 1966. The circuit uses a general-purpose FET that admits an equivalent. The instrument is a 250 uA full-scale microammeter.
This non-inverting AC amplifier was found in the February 1990 issue of Radio Electronics...
This sensor circuit for a small robot was found in a Popular Electronics from the 90s. The circuit...
This direct detection circuit was found in a 1986 documentation. The output is of low power, but...