Current indicator (CB22132E)

In this circuit the voltage across the LED is limited by the diodes. The maximum current also depends on the resistor.

High gain amplifier (CB23897E)
This is an amplifier with one of the first integrated circuits available, the CA3020 which was...
Differential microammeter (CB7362E)
This circuit was obtained in a 1964 Electronic Design. The transistors are from the era and the...
Tunnel Diode Listening Transmitter II (CB19426E)
This low power circuit for the FM band was found in a spy book from the 90s. The tunnel diode is...