This 1965 circuit uses a Philips 4068 tube to measure extremely small charges. The circuit has as indicator a micro ammeter and the transistors are of the time.
The presented circuit was found in the National Semiconductor FET Databook. The setting applies to other...
This configuration with the LM383 appears elsewhere on this site. The circuit shown was obtained...
This very high input impedance preamplifier is from a publication of 1977 but can also be mounted...