Show sample as: 72-frame QuickTime VR or 360-frame QuickTime movie loop.    My periodic table poster is now available! Rectifier. Before the invention of silicon and germanium rectifiers, selenium was used to convert AC to DC. It worked only marginally well compared to modern silicon components. Source: eBay seller radiocorner Contributor: Theodore Gray Acquired: 25 November, 2003 Price: $10/24 Size: 2" Purity: >90%