This high impedance circuit was found in 1967 documentation by Ferranti. The original operational amplifier is from that time. The circuit can be implemented with modern equivalents.
This simple rain, leak or moisture detector circuit appears in other places on this site with...
This circuit was obtained in a 90s EDN. The components used are from that time. The voltage...
This circuit is from a 1967 General Electric SCR manual. The capacitors are polyester and the...