Radio with amplifier (CB20486E)

We found this circuit in a publication of 1991. The audio amplifier is an operational that admits equivalent.

4 to 20 mA Interface (CB4815E)
This 4-20 mA current interface was found on a 90's EDN. The components used are not common today and...
Motor Speed Control (CB12087E)
This control for low current motors (up to about 100 mA) was found in a 1983 publication. The...
Night Switch (CB12701E)
The circuit shown in the figure activates a small indicator lamp that will start to flash when the...