![]() ![]() To make them work good, it required copper with a very low oxygen content, which is hard to get, and normal electrical copper can not be used. These are made by copper oxide on one side of a copper plate, and then add a conductive layer over the oxide. ![]() In 1925 came Copper Oxide diodes, which look like stacked coins. Next were electrolytic rectifiers, but anything "wet" was always a problem. It would take another 50 years (!) before Selenium rectifiers as we know them, were coming on the market.įirst high power rectifiers were "wet" types. However it resulted from the interest to make photo detectors. In 1878 Werner von Siemens discovered the Selenium diode. A semiconductor effect was already found with crystals of Zinc Oxide, Copper Sulfite, and a few others. Braun, a wireless enthusiast and Nobel Prize winner. ![]() The crystal rectifier, was discovered in 1874 by the German Professor K.F. Strangely however, when advised by people who really know, they begin to argue about it, instead of listening. But if not, what are these people talking about? Only about what they "think" and not about what they know. And from the remaining 5%, I dare say that virtually nobody took the trouble of making a plot of the current as a function of forward and reverse voltage. I do not have the real number for this of course, but I guess that 95% of the Selenium Diode talk is by people who never saw one in reality. So if such is good advice, or ridiculous advice, think about that, before you believe it.īut for replacing Selenium diodes, it's exactly this kind of "knowledge" you can quickly pick up. You will quickly be advised about "sound" by people who only know about Western Electric 300B from internet pictures. Go to any forum and ask for sound difference of Chinese 300B vs. Not understanding the meaning of dynamic resistance, and a few other difficult things.įorums are nice on the one hand, but generally it goes wrong when it's just gut feeling what they are writing about, but pretending to be specialists. They see of a diode to be a switch with 0.7V voltage drop. This becomes more difficult, as reading data sheets is regarded a waste of time in this group of users. I stressed this point at some other places of this website, when using vacuum tube diodes. Typically, anything having to do with diodes, is a field where amateurs feel competent to advise inexperienced people. They're not impossible to find, and even still made (when I write this in 2021) for exact replacement purposes. Consider replacing e a broken Selenium diode, with a good one. However Germanium is too good, because at low current, they work even very nice below 0.3V, which a metal diode does not do very well. REPLACING A SELENIUM RECTIFIER WITH A SILICON DIODE SERIESA closer replacement for a low power metal diode is a Germanium High Current diode like 1N93, with a series resistor. A silicon diode is "dead" below it's threshold limit, but a (single cell) Metal diode begins to work much below 0.7V already. To begin with, a metal diode in the range below 0.7V is superior to Silicon, and not just a little bit. Only, when used in measurement circuits, it becomes a different subject. When it's just for some uncritical power supply, replacement by Silicon is easy of course, assuming you know the consequences of what you are doing, with respect to saturation peaks of the transformer, increased capacitor peak current, and it's maximum AC current, and a few things more that need no explanation. Or worse, they throw out good functioning copper-oxide diodes, which are totally harmless, because they think these are so called dangerous Selenium diodes. You will find quickly in forums, how terrible old Selenium diodes are, how dangerous, and how people try to simulate something with similar characteristics by using a composition of Silicon diodes, Zener diodes and resistors. ![]() Selenium Diodes and Copper-Oxide diodes in old instruments. ![]()
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