The purpose of this circuit found in a 1967 GE SCR manual is to control a heating element. The SCR must have current according to the controlled load.
Found in an English documentation from 1977, this circuit activates a relay when the input voltage...
This Colpitts crystal oscillator was found in an American publication for amateurs in the 1980s....
This multivibrator, whose frequency depends on the capacitors, was found in an Argentine...