Current indicator (CB22132E)

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

Current Limiting Battery Charger (CB19020E)
Some of the components used in this circuit are not very common today. The circuit is from a 1996...
Quadrature detector (CB21753E)
This circuit was found in a 1977 American manual. The integrated circuit is from the time....
Superheterodyne FM Receiver (CB4334E)
The integrated circuits used in this 1989 project are uncommon today, including the IF coil that...