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 turns on and off when a short pulse is applied by SW to the input of the first...
We found this circuit in a publication of 1991. The audio amplifier is an operational that admits...
The oscillator of the figure has its frequency determined by the crystal. The indicated value is...