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 causes an LED to flash at a frequency determined by the capacitor. The circuit is...
This simple 1-transistor receiver has speaker listening. We found it in an article published in...
The integrated circuit used is equivalent to the 555 and the transistor can be the BC558. R1 and...