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.
It is an improved version of the previous circuit with a voltage follower that reduces the load...
This circuit activates a relay when the water reaches the sensors. The circuit is from a Radio...
This circuit is from an American transistor book from the 60's. The transistor is germanium of the...