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Saturday, October 2, 2021


Selenium rectifiers. The name kind of sounds like Dilithium crystals, possibly related to flux capacitors. 

Anyway, there were two of them in the Globe Electronics V-10 VFO Deluxe that I recently bought.  Obviously they had to go, so I took them out yesterday, replacing them with a 1N5408 silicon rectifier.  

The new diode had a significantly lower voltage drop than the selenium rectifiers -- this pushed the output voltage from the power supply up to around 200V.  It is supposed to be around 185 V.  So I put a 470 ohm,  5 watt resistor (found in the junkbox) in series.   This brought the output voltage to 167 V.  Close enough.  VFO seems to be working fine.  

I'm glad I did the extraction before these aging components released their nasty toxic smoke. 

W3HWJ has a good article on replacing these nasty old parts, with some interesting info on their history:   http://www.w3hwj.com/index_files/RBSelenium2.pdf

Backgound on the element Selenium:  https://en.wikipedia.org/wiki/Selenium


  1. I remember a friend in my high school radio club who took a selenium rectifier apart and then demonstrated that those individual fins could be used as photocells.

    Destructive but more useful than our usual club activity of plugging a tube into the tube tester and making the filament go super-nova

  2. That sounds like a great high school club. I thought about doing something like that when I read about the properties of Selenium. 73 Bill

  3. It was a fun club but on a downward glide in 1973. The club and alumni were active on Field Day though: http://wb9kzy.com/ggg.htm We had a lot of energy those days :)

  4. Why not use two diodes in series.
    Then you won't get any heat build up from the dropper resistor.

  5. Nemo: The problem is that they Selenium rectifiers have a much larger voltage drop than the silicon diodes. So two silicon diodes would only drop about 1.2 volts total. The Selenium diodes drop about 5 volts each. That's why you need the resistor. 73 Bill


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