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.
The microphone for this circuit, found in a 1967 Japanese documentation, must be ceramic or...
Found in National Semiconductor documentation from the 1990s, this circuit produces a tone to be...
This tuned circuit was found in a 1966 Electronic Circuit Handbook. The transistor can be any...