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 Post subject: Killer Seleniums
PostPosted: Dec Sat 11, 2004 12:33 am 
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You have GOT to be joking....<P>------------------<BR>


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 Post subject: Killer Seleniums
PostPosted: Dec Sat 11, 2004 2:20 am 
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Location: ayer ,ma usa
Hey, these things are totally dogs, face it, Alan is right on. As for foreign ones being "better" I hope Walter is around. The ONLY thing I have seen go wrong (ever)(beyond extremely frustrating dial cords) in maybe 30 European radios I have repaired is that tiny selenium rectfier, either the Siemens one in the flat shiny can ,or the round one that looks like a cap with four leads. I think late European radios, Grundig and Blaupunkt, are much better sounding than ours, but the styling is brutal(to me) except for the Blaupunkt small table model, which is a vacuum tube KLH, really. The European seleniums only go "tink" when they hit the can bottom, but hit the bottom they do. Even a 35W4 is better than these, and they are not so good. Another example...Pilotuners. I fixed maybe 25 of those , all had burned out, or half burned seleniums due to shorted filters, which sometimes takes the small power trans, too. And Motorola TV-7's ? There is not a single one on earth that really works still with original seleniums; same with GE 10" ,the one with 19BG6 in it.Those who have seen one fail not only won't forget smell, I won't forget the fireworks that erupt all over the plate, like little volcanoes, until it burns open near the middle washer. But ,some people like cold water showers and gas lighting. To each his own<P>------------------<BR>


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 Post subject: Killer Seleniums
PostPosted: Dec Sat 11, 2004 3:11 am 
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Location: Florence, Al. U.S.A.
I recently retired from a chemical plant that uses 440VDV @ 115,000 amps. The rectifiers are SILICON. I personally think the leap from Selenium to Silicon was a giant step forward. I do miss the intoxicating aroma of a smoking selenium rectifier, though. <P>------------------<BR>


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 Post subject: Killer Seleniums
PostPosted: Dec Sat 11, 2004 8:37 am 
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Location: Warwick,RI
I suspect that fear of **possibly**being exposed to the smell has prompted people to replace perfectly good seleniums.I never heard of anybody's house burning to the ground because of a bad one.<BR>I burned one up one time by screwing up and making a wrong wiring connection in a power supply.I did survive quite well,however and the odor while not very nice cleared out completely overnight.<BR>I would not put plates from a selenium in my morning corn flakes but our society has gone totally crazy with overly stated precautions in some areas(probably motivated by a fear of bring sued in some cases)and I doubt that any man ever lost his virility from sniffing a burned selenium<BR>or suffered permanent bodily damage of any kind unless he bathed in a solution of water and se plates for 24 hours,non-stop.<BR>Malcolm<P><BR>Malcolm<P>------------------<BR>


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 Post subject: Killer Seleniums
PostPosted: Dec Sat 11, 2004 11:01 am 
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Location: glenview,il usa
Norm, <P>You guys have me intrigued! I can't wait to wire one up in series with 110 volts... <P>Bill<P>------------------<BR>Bill - KC9CVW


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 Post subject: Killer Seleniums
PostPosted: Dec Sat 11, 2004 12:06 pm 
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Location: Vieques, PR, USA
A bit of diversion from electronic uses of selenium but I got a good story from a rancher in Wyoming about the problems with naturally occuring selenium in the 'soil' (thats a misnomer for poisioned rock that is so prevalent out there.)<BR>Apparently some areas have very high selenium content in the soil. In this particular area (Alcova, west of Casper) the landowner was required to replace the entire irrigation system on their property so as to "sprinkle" the expensive and scarce irrigation water in a manner that doesn't cause the selenium (in particular) to leech to the top of the soil.<BR>The selenium present in grazing fodder can kill a herd of animals in a heartbeat...symptoms not unlike Mad-Cow Syndrome or MS in humans. Not pretty. <BR>Its a big issue out there but so is water.<P>I suppose its not unlike the asbestos hoopla of the 70s. Too much of anything can be bad. You can hyperventilate to death in crisp mountain air or drown in a cupful of spring water so the "I'm gonna die if I can't get my hands on some 1N4007s" is a bit overstated.<P>At the end of the day, the Plain Jane Se rectifer is a POS just because it was an unreliable component and could be expected to fail at any moment with memorable consequences.<P>Apart from that, I suppose they're okay.<P>-Bill<BR><P>------------------<BR>


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 Post subject: Killer Seleniums
PostPosted: Dec Sat 11, 2004 12:20 pm 
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I am shocked they do not blame the soil troubles on that 50KW flamethrower KTWO out there in Casper.<P>If the health cops think that Selenium is dangerous in the home, I wonder what they would think of the glow-in-the-dark radiating original meters on my R390A....<P>------------------<BR>


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 Post subject: Killer Seleniums
PostPosted: Dec Sat 11, 2004 12:35 pm 
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Entertaining thread <IMG SRC="http://antiqueradios.com/forums/smile.gif"><P>As usual, I think the truth is not at the extremes...<P>From the collective knowledge on this forum, it's clear that Se rectifiers do fail, and fairly frequently (although I myself have not encountered a bad one yet). On the other hand, it is certainly not the case that 100% of Se rectifiers out there are bad and have to be replaced before you dare apply power.<P>I see it this way:<P>1. If you want maximum reliability in your antique radio or TV, replace the Se rectifiers.<P>2. If you enjoy keeping your radios and TVs as close to original as possible, leave them in until they fail.<P>3. The odor is reported to be very unpleasant, but I cannot find anything (including Alan's citation from the chemical safety manual above, which I believe is still valid and reasonable) that suggests it is dangerous to catch a whiff of the stuff for a short time period. Don't eat your Se rectifiers, and don't smoke them in your pipe. Open the window if one blows. It is true that trace amounts of Se are necessary for good health.<P>Do what you like -- it depends on what your goal is: maximum reliability or maximum preservation. No one can tell you that one of those two goals is the best for everyone. <P>(I do suspect, however, that all these radios we are "restoring" today will become less valuable in the future than those that still have their original components, even if nonoperational.)<P>Tom<P>------------------<BR>


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 Post subject: Re: Killer Seleniums
PostPosted: Aug Mon 31, 2020 4:36 am 
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This is an interesting discussion which I know is an old one. As far as hazardous, there is an extensive MSDS on Selenium Dioxide. Nothing to simply put of as old wives' tales. In addition, the bad devices should never make it to the landfill. Consider hazardous waste.

I have attached the MSDS for your files if interested.
Well I did try... something about extension not allowed (PDF)

Let's try this instead:
https://www.fishersci.com/store/msds?pa ... anguage=en

Enjoy
Dave KB7GP

Attachment:
SELENIUM-dioxide.pdf [55.79 KiB]
Downloaded 25 times

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 Post subject: Re: Killer Seleniums
PostPosted: Aug Mon 31, 2020 8:03 am 
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I'm rather fond of selenium rectifiers.

For one thing they have a much larger physical mass to a silicon diode rectifier and as a result a lower thermal resistance. They act like a power germanium rectifier and with the equivalent of a series resistor. This higher forward resistance is often helpful and in many designs, the classic being the Lead Acid battery charger, they could be used with the power transformer and only a little added series resistance. This made the whole assembly simple and the heat dissipation was handled on the large surface area plates of the selenium rectifier.

Also, unless terribly abused they are one of the most reliable items on earth. I have some in apparatus I power nearly every day, over 50 years old and they are still fine.So they certainly do not need to be replaced on sight, unless you think the Moon landing was filmed in a Hollywood basement and that crops circles were done by Aliens and not Humans.


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 Post subject: Re: Killer Seleniums
PostPosted: Aug Mon 31, 2020 5:42 pm 
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This is a really stupid thread. Selenium rectifiers are as dead as buggy whip sockets. Get over it and move on.


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 Post subject: Re: Killer Seleniums
PostPosted: Aug Mon 31, 2020 5:46 pm 
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"Killer Seleniums" would make a good band name...


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 Post subject: Re: Killer Seleniums
PostPosted: Aug Mon 31, 2020 8:43 pm 
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There was a movie about a husband killing his wife with selenium and other poisons (Lethal Vows). And another about a guy who slowly killed his wife with selenium he scraped of selenium rectifiers. If I remember right, he left the evidence of disassembled selenium stacks in the basement.
No reason to get rid of the selenium stacks unless you have someone who wants to slowly and cruely dispatch you.

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 Post subject: Re: Killer Seleniums
PostPosted: Aug Mon 31, 2020 9:53 pm 
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tym wrote:
"Killer Seleniums" would make a good band name...


Yes, and maybe some lyrics for a cover song to get the band started: "Heat me up, but I won't die, I am Selenium...bullet proof, nothing to lose, fire away fire away.. etc"

One interesting thing is that in Australasia Selenium rectifiers were relatively rare in appliances, radios TV etc, because in most cases, our sets used 240V input power transformers and full wave tube rectifiers and were not AC/DC types with half wave rectification. Where as in the USA, many small radios and TV's etc used them.The common places they turned up here were mainly in battery chargers (pre the days of silicon rectifiers) and in that application they were amazingly hardy and put up with all manner of abuse.


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 Post subject: Re: Killer Seleniums
PostPosted: Aug Mon 31, 2020 10:28 pm 
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pauls.ironhorse wrote:
There was a movie about a husband killing his wife with selenium and other poisons (Lethal Vows). And another about a guy who slowly killed his wife with selenium he scraped of selenium rectifiers. If I remember right, he left the evidence of disassembled selenium stacks in the basement.
No reason to get rid of the selenium stacks unless you have someone who wants to slowly and cruely dispatch you.

I prefer to use ricin when I do my murders. Less traceable and tends to throw suspicion onto the KGB. Selenium is strictly for amateurs and electrical engineers.


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 Post subject: Re: Killer Seleniums
PostPosted: Aug Mon 31, 2020 10:59 pm 
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ACORNVALVE wrote:
tym wrote:
"Killer Seleniums" would make a good band name...
One interesting thing is that in Australasia Selenium rectifiers were relatively rare in appliances, radios TV etc, because in most cases, our sets used 240V input power transformers and full wave tube rectifiers and were not AC/DC types with half wave rectification. Where as in the USA, many small radios and TV's etc used them.The common places they turned up here were mainly in battery chargers (pre the days of silicon rectifiers) and in that application they were amazingly hardy and put up with all manner of abuse.

An interesting counterexample is Germany, which used full-wave selenium rectifier modules in tons of 240 VAC radios with power transformers in the 1950s and 60s.

I still think my summary a few posts up (from 16 years ago) is about right. In the intervening years, I have seen a few selenium rectifiers with low efficiency (too much back leakage), but I still see most of them working just fine. When restoring for others (most of my work), I replace them. In my own stuff, I sometimes leave them.

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 Post subject: Re: Killer Seleniums
PostPosted: Sep Tue 01, 2020 2:06 pm 
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Huh, I'm glad you brought this up and mentioned the landfill. Just the other day I pulled a working one out of a Zenith and it made a thunk when it hit the bottom of the garbage can. Everything I read about the subject said pull it out as if it was a stick of dynamite with the fuse about to be lit. After reading through this thread I retrieved the unit from the can and put it in my parts bin. I almost wish I had kept it in the radio. I ended up using a 10-watt dropping resistor to get my B+ correct, a big ceramic brick, it was the only one I had at 50 ohms. It looks pretty ugly in there but I guess I don't have to worry about it overheating. I don't know, maybe it was better that I did pull the selenium out. The radio is being used in an office. I can imagine the drama that would ensue and the people who would have become involved had the thing smoked for whatever reason. :!: :!:


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 Post subject: Re: Killer Seleniums
PostPosted: Sep Tue 01, 2020 3:22 pm 
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I have been replacing them with silicon diodes for many years. A long time ago, I got a bag of 2.5 amp 1kv diodes from a guy who was closing his shop; I still have plenty in stock.

Years ago, I worked with a technician who called selenium rectifiers "stink cells".

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 Post subject: Re: Killer Seleniums
PostPosted: Sep Tue 01, 2020 4:14 pm 
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I have only had one fixer where a metal rectifier in a Thorn stereogram, was associated with a massive catastrophic failure. In this one it was a chain reaction. The prognosis as I see it, was a 6GW8 shorted; That overloading "B" caused the metal rectifier to short, which in turn caused the secondary to burn & melt. This also burnt the dial string, it got that hot. Hot material fell onto the fuse holder (below chassis) and melted part of it.

As there was insufficient load on the primary, (5A factory fuse 240V supply) that held and because there was no issue primary side, the circuit breaker & GFCI (RCD here) held.

Had the owner not seen the smoke signals, it was pretty clear that the probability of a house fire was high. The only other that I believe was metal, which slowly died, was the EHT rectifier in my Heathkit OS-1.

Roberts R66, (fixer set), has one metal rectifier for "B" and an other for "A" (filaments). Both working, left well alone; One only paper cap in it, leaking: Bin. New LV electrolytics, HV Ecaps tested good: Left in. Used it for an article in Australia's "Silicon Chip" magazine. Sent home.

Marc


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 Post subject: Re: Killer Seleniums
PostPosted: Sep Tue 01, 2020 10:28 pm 
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HaroldJenkins wrote:
The radio is being used in an office. I can imagine the drama that would ensue and the people who would have become involved had the thing smoked for whatever reason. :!: :!:


Wee you see, the obvious solution, for a selenium rectifier in a half wave application:

The forward voltage drop of a silicon rectifier is less than one volt most of the time and the power dissipation and reverse leakage is negligible at HT currents used in radios. So , if you simply place a silicon rectifier in series with the feed to your beautiful selenium rectifier masterpiece (I use diodes like the BY228, because of their very high piv rating superior to a 1N4007 and better for line voltage use), then it doesn't matter how sick or reverse leaky your selenium rectifier is, the circuit will still work properly and do its job dissipating the heat via its fins, without going into a mode where it smokes out the office. So it makes the radio look original and its safer than before.

You can do this with full wave arrangements to by adding two or 4 silicon rectifiers depending on the circuit configuration and keeping the original selenium rectifier and you don't have to add an additional resistor. This assumes of course that the selenium rectifier was basically working in the first instance and not already smoked up or shorted out.


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