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Small Selenium Diodes: Practical Uses?

Wirth's Law

Member
I recently purchased a few selenium rectifiers. The few technical resources I could find about them say they were mostly used in high-voltage systems like voltage multipliers for cathode ray tube (CRT) television, railroad signaling, etc. A few that are still commercially available today have working reverse voltage ratings well over 5 kV.

I also found some very small selenium rectifiers (see the attached image). These seem to have much smaller voltages in mind. There is not a lot of information about where these are used or if they excel at anything in particular. After characterizing one sample with a multi-meter, it looks like this contains 4 rectifiers. Two of them share a single cathode (K) pin, the other two rectifiers are independent. There's not a whole lot of information on the web about it...just a few mechanical drawings, plus the statistics I included to the photograph.

Does anyone know how this style of miniature selenium rectifier is being used? I've included a U.S. penny for scale...

Selenium Rectifier NTE120.jpg
 

Wirth's Law

Member
Okay. I forgot to mention, the original packaging did mention TV color convergence. It sounds like color convergence was meant to get the CRT beams for red, green, and blue images to align properly. To avoid something like this...

stereoscopic3DAdjust.png

If this is true, then were selenium diodes better suited than other diodes for this type of use?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Okay. I forgot to mention, the original packaging did mention TV color convergence. It sounds like color convergence was meant to get the CRT beams for red, green, and blue images to align properly. To avoid something like this...

View attachment 121205

If this is true, then were selenium diodes better suited than other diodes for this type of use?
Presumably so - however, I've repaired thousands of colour TV's, and wasn't even aware that selenium diodes were used - so they obviously never failed in that situation.

As for convergence you had both static and dynamic convergence to set up, as well as purity - it was really a pain until PIL tubes arrived.
 

ronsimpson

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Just because these diodes were used in TVs does not say they were commonly used. ( or used in the last 40 years ) I used silicon.
 

Nigel Goodwin

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Most Helpful Member
Just because these diodes were used in TVs does not say they were commonly used. ( or used in the last 40 years ) I used silicon.
Well 'nothing' was used in the last 40 years, as convergence adjustment was gone by then :D - except for Sony Trinitron who never went PIL, but they were in-line and didn't have the masses of adjustments of the original delta tubes.

Anyway, as for the original question - find a bin and throw them in!.
 

Wirth's Law

Member
Since I have them I figure I'll at least characterize them and see how they perform versus silicon. These aren't the type of high-voltage selenium rectifiers I'm used to reading about and they are apparently effective at low voltages.

I'm actually having a hard time finding TV schematics that might hint at the exact circuit role these would have had. I did find one U.S. patent from 1969 that looks promising. It has a color convergence (sub) circuit that uses exactly 4 diodes, and 2 of them have connected cathodes just like this sample. I'll give it a closer look later this week. If anyone's interested, its US3631296A.
 

gophert

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Selenium diodes have a nice acrid odor when they blow. They also have a much higher voltage drop than silicon.

Wirth's Law
Are you interested in a 5kV or 15kV selenium rectifier? I think I have a few NOS still in the blister package.
 

dr pepper

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Also used in Tv's in the horizontal sync circuit.
They have a low forward voltage so would be good in things like Am receivers as the detector diode, and maybe for a precision rectifier in test gear.
 

Nigel Goodwin

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Also used in Tv's in the horizontal sync circuit.
They have a low forward voltage so would be good in things like Am receivers as the detector diode, and maybe for a precision rectifier in test gear.
Are we back to 50's now? - it's been a hell of a long time since diodes were used in flywheel sync circuits. Although to be fair there 'may' even have been an odd transistor set or two which did, but not selenium. I obviously repaired many such sets, but I don't recall any having selenium diodes in the flywheel sync?.

Only fit for a skip - get them binned! :D
 

dr pepper

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C'mon nige, some people collect 50's sets, like me.
And yes in the ear;y 60's selenium's were sometimes used, most of which are now defunct, the diodes that is.
 

Nigel Goodwin

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C'mon nige, some people collect 50's sets, like me.
And yes in the ear;y 60's selenium's were sometimes used, most of which are now defunct, the diodes that is.
Well I repaired plenty of early 60's sets, and don't recall ever seeing any? - my main experiences of selenium rectifiers were replacing mains ones with a BY127, a wirewound resistor, and a small piece of tag strip - and of course replacing hundreds of smelly EHT ones.

For those of you who have never done TV repairs, you go to the house, the lady opens the door, and you say "I'll just nip back to the van and get the part" - no need to go in the house, never mind see the set :D
 

unclejed613

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Selenium diodes have a nice acrid odor when they blow.
selenium oxide smells like sulphur burning (rotten eggs). i was informed in the Army that the fumes are hazardous and do be avoided. selenium rectifiers do not age well, and need to have the plates "re-formed" (much like electrolytic caps that have been in storage or idle for a long time) if they have been sitting idle. the thing i never liked about selenium rectifiers was the relatively high reverse leakage current. a lot of antique radio rebuilders bypass them with a 1N4007, and leave the stack in place for visual accuracy.
 

Wirth's Law

Member
Selenium diodes have a nice acrid odor when they blow. They also have a much higher voltage drop than silicon.

Wirth's Law
Are you interested in a 5kV or 15kV selenium rectifier? I think I have a few NOS still in the blister package.
Yeah, I might be able to depending on the type.

I did notice the high reverse leakage with some high voltage Se diodes. I haven't tested the small ones yet. I'll see if I can use the blue diodes in something this weekend.
 

dr pepper

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Stuff them across your meter & measure Vf to make sure they are what they say.
 

KeepItSimpleStupid

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I hate those things and I really hate the smell. More effort has gone into replacing them. BUT you have to add a large series resistance
 

JimB

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selenium oxide smells like sulphur burning (rotten eggs).
That is to be expected, sulphur and selenium are next to each other in the same column of the periodic table.

i was informed in the Army that the fumes are hazardous and do be avoided.
I was once working with an old battery charger and managed to release some of the foul smell from the selenium rectifier. A few hours later I felt rather ill. The next morning the feeling had gone away. Thankfully.

JimB

Edited for typo.
 
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