page_title: Selenium rectifier
section_title: Use
hierarchical_section_title: Selenium rectifier / Use
caption_attribution_description: English: Mallory selenium rectifier from 1960s. Each plate is 1 inch square. I took this photograph of an artifact in my possession.
context_page_description: A selenium rectifier is a type of metal rectifier, invented in 1933. They were used in power supplies for electronic equipment and in high-current battery-charger applications until they were superseded by silicon diode rectifiers in the late 1960s. The arrival of the alternator in some automobiles was the result of compact, low-cost, high-current silicon rectifiers. These units were small enough to be inside the alternator case, unlike the selenium units that preceded silicon devices.
  The rectifying properties of selenium, amongst other semiconductors, were observed by Braun, Schuster and Siemens between 1874 and 1883. The photoelectric and rectifying properties of selenium were also observed by Adams and Day in 1876 and C. E. Fitts around 1886, but practical rectifier devices were not manufactured routinely until the 1930s. Compared with the earlier copper-oxide rectifier, the selenium cell could withstand higher voltage, but at a lower current capacity per unit area.
context_section_description: Radio and television receivers used them from about 1947 to 1975 to provide up to a few hundred volts of plate voltage. Vacuum-tube rectifiers had efficiencies of only 60% compared to the 85% of selenium rectifiers, partially because vacuum-tube rectifiers required heating.  Selenium rectifiers have no warm-up time, unlike high-vacuum rectifiers. Selenium rectifiers were also cheaper and simpler to specify and install than vacuum tubes. However, they were later replaced by silicon diodes with high efficiencies (close to 100% at high voltages). Selenium rectifiers had the capability to act as current limiters, which can temporarily protect the rectifier during a short circuit and provide stable current for charging batteries.
caption: Selenium rectifier from 1960s. Each plate is 1-inch square.
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