This 4-tube counter was found in Radio Electronics magazine from December 1959. The circuit uses a coil as a sensor to detect the passage of metallic parts or magnets.
Found in documentation from the 1980s, this circuit applies to other 3-terminal voltage...
This low power circuit for the FM band was found in a spy book from the 90s. The tunnel diode is...
This very simple configuration produces the sound of a space gun or laser. The circuit uses common...