This Kirlian machine circuit uses a car ignition coil. The circuit is from a Radio Electronics from May 1986. It is mentioned in an article that teaches how to obtain photographs.
This circuit, from the 90's, is intended for operation with vinyl record players of the time, as...
Using a zener diode it is possible to change the linearity of the scale of an analog instrument by...
Found in American documentation from the 1980s, this circuit prolongs the ringing of a doorbell or chime...