This circuit was found in the January 1991 issue of Radio Electronics magazine. The circuit uses integrated circuits of the time and the coils depend on the tuned bands.
This circuit that draws 1 out of 8 LEDs was found in an 80's American documentation. The circuit...
This protective circuit for power lines was found in a Radio Electronics from November 1957. The...
In figures 1 and 2 we have two current drains that can be made with operational amplifiers and...