What ever happened to Selenium rectifiers?

What ever happened to Selenium rectifiers?

It seemed they had a short life span in the 60s and then just vanished.

They were cool looking devices, and seemed to work well, eliminating a tube, and thus saving on power consumption to heat the filament of the tube. I never did fully understand how they worked, I never could understand how the electricity jumped across the plates, and why the bolt that held them together did not just act as a straight thru conductor since there did not appear to be any insulation around it.

Reply to
boomer#6877250
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This should be in sci.electronics.basics

What happened to selenium rectifiers was silicon. Around the era of seleniu m, it seems that they were used for higher voltages and copper oxide was us ed for lower voltages. strictly from memory here, the selenium jobs had som e leakage and alot of forward drop. That made them more suitable for higher voltages, like B+. (a summary of that term later) the copper oxide ones, I IRC had alot of reverse leakage but less forward drop, making them more sui table for lower voltages.

If you take apart any of these old rectifiers and examine them very closely you will see that they are insulated from the bolt, and that is why it doe s not constitute a short circuit. Sometimes it is just a little eentsy ween tsy insulator that you almost don't think would do it. but then the dielect ric strength of air is something like 600 volts per thousandth of an inch a t STP. Or something like that. High moisture or anything in the way of a co ntaminant reduces this insulative quality.

Selenium rectifiers did save a filament source, and that was a fairly highl y isolated source because usually that filament supply has to be at B+ pote ntial. Tubes like I think 6X4 or whatever with the indirectly heated cathos de no, but they had their ow limitations when it came to heater to cathode voltage. so for the major voltages, like for a power amp they stuck with li ke %u4s n shit and just dealt with the insulation in the power transformer. Note that most selenium rectifiers could not put out enough current for a high powered amplifier.

Actually, to this day, audiophile tube amps are built and they usually go w ith tube rectification. The tube rectification has some resistance in it an d reduces ground currents and therefore hum. Selenium is almost the same ex cept for its failure mode. When a 5U4 fails, you go online and buy a 5U4, w hen a selenium rectifier fails you evacuate the house for a month and buy a ll new furniture. at least these days. Like these assholes with second hand smoke causes more death than to the smoker, nothing could be more ridiculo us. but people cannot stand smell. we went from taking a bath in the same w ater as our brothers and sisters on Saturday once a week to taking three sh owers a day. these people, one selenium rectifier failure and they would pr obably have the house condemned.

It has been described as rotten eggs but there is more to it, something lik e a tinge of boiling battery acid mixed in.

So basically they were dropped like a hot potato ASAP. People could stand i t back then, and as an advantage when they called the TV or radio repairman and said "It smells like rotten eggs" the guy knew what parts to bring.

The B+ thing is about old battery operated tube equipment. the A battery fe d the filaments and was maybe 3 volts or whatever, while the B battery supp lied the plates and other higher voltage needful sources, many of them were 90 volts. I read somewhere that some units had a C battery but have not fo und any evidence of this and I can't think of why. Grid bias maybe ?

Anyway, if you ever have to replace selenium rectifiers, you need some resi stance in series. First of all, stuff that old is designed to run on 110 vo lts and nominal US voltage is now 125. What's more the better efficiency ta kes it up even higher. You could easily find your tubes replating all over the place if you don't cut it down, and this takes power resistors.

Reply to
jurb6006

They stunk. well, compared to silicon.

They didn't suck as much at tubes did. (I think I'm out of puns now)

the bolt only touched the top and bottom plate.

it's just the loop of a bridge rectifier unrolled into a straight line, with the bolt connecting the two ends.

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Reply to
Jasen Betts

fed the filaments and was maybe 3 volts or whatever, while the B battery su pplied the plates and other higher voltage needful sources, many of them we re 90 volts. I read somewhere that some units had a C battery but have not found any evidence of this and I can't think of why. Grid bias maybe ?

grid bias batteries:

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NT

Reply to
tabbypurr

They had a short life span!

Nasty, expensive, inefficient, leaky, smelly.

Wikipedia has the details.

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John Larkin         Highland Technology, Inc 

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Reply to
John Larkin

Did they have a short lifespan? I thought they were considered to be fairly robust and could take a fair amount of punishment. Also negligible reverse recovery time but that doesn't matter so much in a tube power supply.

I think they're still used as TVSes...

Reply to
bitrex

They produced nasty curls of smoke when failing ;-)

Any idea where one might get unpainted plates today?

I'd like to do a photo cell experiment. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

Litterally stunk. Silicon just smells a little fishy.

Reply to
krw

Better than toobs, crappy compared to silicon, thus, short life.

The basic physics is that they're a junction diode, just a much crappier one than silicon. I'm not sure that there's much detail out there beyond that, given how short a commercial life they had.

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Reply to
Tim Wescott

I wouldn't define that smell as "fishy"... it was gawd awful ;-) ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

My father had a car battery charger (with a selenium rectifier) which lasted at least four decades.

Reply to
Clifford Heath

Crikey! They were in radio and TV sets for _many_ decades.

I grew up in a radio and TV repair shop in that era... did many a smelly replacement ;-) ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

I'm pretty sure there are many thousands of battery chargers and (especially) welders using Se rectifiers still in service. Those old AC/DC welders would last forever. The newer ones are chock full of electronics and will be in the landfill before you know it.

They certainly let you know when they failed.. hmmm.. they contain cadmium so not very RoHS-y. Cadmium metal has the best conductivity for conductor mass figure of merit- significantly better than copper.

--sp

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Reply to
Spehro Pefhany

If you don't need it flat, maybe an old photocopier drum?

--sp

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Reply to
Spehro Pefhany

This was the main radio I used in college to listen to my favorite communist college radio punk rock stations:

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IIRC it was manufactured in 1961. It was still working fine as of 1999 on what looked like the original set of tubes and selenium rectifier. The output tube (35C5) might have not been original - those got blazing hot and there was aluminum shielding above it to prevent the wood from being scorched.

Reply to
bitrex

Back in the ~80's there was a train derailment near by. I and a buddy went to look over the wreckage and pulled some circuit boards from the diesel engine. All I remember are Se rectifiers, big resistors, and relays.

George H.

Reply to
George Herold

Those were smell based rectifiers :-) :-).

You very hard tried to escape from the room that had been used by the (overloaded) selenium rectifier.

You absolutely tried to avoid going into the room where such selenium rectifiers had been used.

Thus unidirectional (person) flow.

Reply to
upsidedown

One episode of the old 'Mission Impossible' TV show had their tech expert replacing a failing Selenium Rectifier stack, during one of their con jobs.

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Reply to
Michael A. Terrell

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