With this circuit found in an American documentation from 1969 it is possible to vary the selectivity (Q factor) of a tuned circuit. The operational is from that time.
This circuit uses a Hall device from that time as a sensor. The circuit is from an English...
Found in Radio Electronics from the 90s, this siren finds many variations on this site. The...
This audio generator that produces both rectangular and sinusoidal signals was found in a...