This TTL circuit is from a Radio Electronics magazine from February 1973. The circuit must be powered with 5 V and the maximum frequency depends on the TTL integrated circuit.
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....