- Replacing a selenium rectifier with a silicon diode install#
- Replacing a selenium rectifier with a silicon diode series#
Selenium Rectifier Handbook 2nd Ed Federal Telephone and Radio 80 pages 1953. The logic family was packaged on SMS cards. Several years later the selenium diodes were found to be not reliable and were replaced by silicon diodes. Nearly any static logic function that yielded one output could be achieved with one transistor and a handful of cheap diodes. The two-level logic was similar to the PLAs programmable logic array that would come on the market many years later. To solve this problem, a selenium diode was connected around the base–emitter to slow it down. The alloy transistor proved to be too fast for the selenium diode recovery. The family was called SMAL or SMALL, for "selenium matrix alloy logic".
Replacing a selenium rectifier with a silicon diode series#
A design was achieved for a DDTL circuit with two levels of diode logic feeding one alloy transistor and no series input resistor or speed-up capacitor. GE claimed that they could make reliable selenium diodes. It was possible to punch 1/8-inch discs from a sheet of selenium diode. The terminal development departments were begging for low cost and did not need speed.
In 1961 IBM started developing a low-speed computer logic family that used selenium diodes with similar characteristics to silicon but cost less than one cent. They are still manufactured for exact replacement purposes, but are not designed into new equipment. During the 1960s they began to be superseded by silicon rectifiers, which exhibited lower forward voltage drop, lower cost, and higher reliability. By far the most common failure mode was a progressive increase in forward resistance, increasing forward voltage drop and reducing the rectifier's efficiency. During catastrophic failure they produced significant quantities of malodorous and highly toxic fumes that let the repair technician know what the problem was. Selenium rectifiers had a shorter lifespan than desired. Selenium rectifiers have an operating temperature limit of 130 ☌ and are not suitable for high-frequency circuits. Each cell can withstand a reverse voltage around 25 volts and has a forward voltage drop around 1 volt, which limits the efficiency at low voltages. The rectifier can show some unforming of the rectifier characteristic after long storage. Selenium rectifiers have a long but not indefinite service life of 60,000 to 100,000 hours, depending on rating and cooling. 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.Ī selenium rectifier is about the same size as a copper-oxide rectifier, but is much larger than a silicon or germanium diode. However, they were later replaced by silicon diodes with high efficiencies (close to 100% at high voltages).
Replacing a selenium rectifier with a silicon diode install#
Selenium rectifiers were also cheaper and simpler to specify and install than vacuum tubes. Selenium rectifiers have no warm-up time, unlike high-vacuum rectifiers. Vacuum-tube rectifiers had efficiencies of only 60% compared to the 85% of selenium rectifiers, partially because vacuum-tube rectifiers required heating. Radio and television receivers used them from about 1947 to 1975 to provide up to a few hundred volts of plate voltage. Compared with the earlier copper-oxide rectifier, the selenium cell could withstand higher voltage, but at a lower current capacity per unit area. Fitts around 1886, but practical rectifier devices were not manufactured routinely until the 1930s. The photoelectric and rectifying properties of selenium were also observed by Adams and Day in 1876 and C.
The rectifying properties of selenium, amongst other semiconductors, were observed by Braun, Schuster and Siemens between 18. These units were small enough to be inside the alternator case, unlike the selenium units that preceded silicon devices. The arrival of the alternator in some automobiles was the result of compact, low-cost, high-current silicon rectifiers.
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. An 8-plate 160 V 450 mA Federal brand selenium rectifierĪ selenium rectifier is a type of metal rectifier, invented in 1933.
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