English: Two General Electric Tungar rectifier bulbs from 1917. The lefthand one is rated at 2 amperes and the right at 6 amperes. These consist of a glass bulb filled with low pressure argon gas, containing a tungsten filament and a carbon pellet anode. Ionization of the gas reduced the forward ("on") voltage to much lower values than could be achieved in the thermionic diode rectifier tube, allowing it to rectify low voltages. It was used as a low voltage rectifier in devices such as battery chargers until it was replaced by selenium diodes before World War 2. Alterations to image: removed aliasing artifacts (crosshatched lines) due to scanning of halftone photo using Gimp FFT filter.