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.
This circuit was found in a Hughes manual of 1068 using a MOSFET of the time. The circuit can be...
Common operational amplifiers like the TL series, CA3140 and others can be used in this circuit...
The transducer used in this configuration that appears elsewhere on this site is a piezoelectric...