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 1966 documentation, this “coin finder” uses components from the era operating at 2.1...
This circuit is from a documentation on the MC1539 from Motorola and may, however, be implemented...
The 747 is an old operational amplifier, but the configuration applies to modern operatives. In...