Found in a September 1972 Radio Electronics magazine, this circuit uses RCA's CA3020, a multi-purpose amplifier in a round metal 12-pin package.
In the figure we have an improved method of varying the voltage of a 7812 regulator. The circuit is...
This 5-range current measurement circuit was found in the September 1989 issue of Radio...
Found in an old English publication this circuit uses a dual gate MOSFET. Coils not specified....