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 contact or reed switch actuation was found in a 1964 Electronic Design. The circuit can be...
This circuit was obtained from a 1985 Electronic Desing. The circuit uses a Darlington which may be...
This configuration that appears several times with variations on this site is from old American...