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 is one of many configurations with a 4-input mixer transistor that can be found on this...
This dimmer was found in the Electronics Experimenter Special projects of 1983. The circuit uses...
The operational amplifier used is the 741, but the configuration is valid for other operational...