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 was found in an Electronics World of 1969. Transistors are general-purpose types. It...
This circuit is from the book Fun Projects for the Experimenter by Newton C. Braga, published in...
We found this alarm in an English publication from 1978. Although the original power supply is 3...