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.
Found in a Popular Electronics from the 90s, this circuit uses thermistors for low noise...
I found this circuit in an old English magazine from 1979, but it can be easily assembled with...
This circuit switches the brightness of the LED. We found it in an English documentation....