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 Post subject: Killer Seleniums
PostPosted: Dec Thu 09, 2004 5:16 pm 
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Location: Mpls, Minnesota
Selenium rectifiers seem to have gotten a bad rap due to misinformation. It has been said you can tell they are bad from the “clunk” they make as the hit the bottom of the garbage can, and they should be replaced immediately on sight. A selenium should never be placed in the garbage can where it will end up in a land fill. I often wonder what the reasons are for attacking the innocent selenium when we have mercury vapor rectifiers, and other materials which are thousands of time more toxic and no mention is made of them.<P>I did a search of the net to find all the bad stuff about selenium rectifiers, and aside from the common sense precautions I didn’t find anything by a reputable source saying they should be replaced because of safety hazards. I did find lots of old wives tales from the dark ages written by wannabe writers who know nothing about the subject. The analogy seems to be, if it smells bad, it must be toxic. Well this is true to a point, when a selenium rectifier is overheated it gives off selenium dioxide gas, which is toxic, and does smell bad. Well this is where the common sense comes in, do we sit and sniff this toxic gas, no, we get away from it to fresh air. The effects from this short-term exposure are usually nonexistent, long lasting effects can be realized from a longer exposure, if you could stand the smell.<P>In reality selenium rectifiers are safe to use and do a very good job. I myself have never found a bad one in a radio, a few weak ones, but never one that had overheated. I have replaced many seleniums in television sets that had overheated but in most cases it was due to bad filter electrolytics. Of course any rectifier tube would have been destroyed under the same circumstances. Many of my radios still have the seleniums and are still working fine after 50 years, with new electrolytics.<P>The major reason seleniums were replaced with silicon is cost, seleniums are still manufactured and used today in rugged high power applications such as welders and power supplies.<P>If anyone has some substantial documented information on why seleniums should be replaced I would like to hear about it. It would be nice to clear up this old wives tale one way or the other.<P>Dave<P>------------------<BR>Intelligence is the ability to use your knowledge


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 Post subject: Killer Seleniums
PostPosted: Dec Thu 09, 2004 6:31 pm 
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Location: Freeport, LI, New York 11520
Hi Dave...<BR>I have a fairly large stock of selenium rectifiers for repair use and have never hesitated to use them as replacements. And, I've never had a callback from a customer on said item. For the most part, they are expensive and where a diode will do the same job, the latter will be the obvious choice.More times than not, the input cap in the power supply was the culprit of the S/R dying in the first place.<P>Happy Holidays!<P>...Jim<P>------------------<BR>


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 Post subject: Killer Seleniums
PostPosted: Dec Thu 09, 2004 9:05 pm 
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Location: Livermore, CA
Hi Dave<P> You may be right about selenium not being very toxic? If not overloaded and voltage drop doesn't increase very much selenium rectifiers operate a long time.<P> I have been around many bad selenium rectifiers. You don't want to be in the same room when one burns. The smell is something a person will never forget. <P> If you are not familar with the smell wire a selenium rectifier in series with a 100 watt bulb to the AC line. It will burn.<P> Over time selenium rectifier voltage drop goes up even without use. This will eventually cause it to fail. Might be like caps getting leaky on the shelf? <P> <P> <P> <P>------------------<BR>Norm


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 Post subject: Killer Seleniums
PostPosted: Dec Thu 09, 2004 9:10 pm 
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Location: Cedarville OH USA
I've had NOS seleniums that seem to be pretty "leaky" myself.<P>------------------<BR>


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 Post subject: Killer Seleniums
PostPosted: Dec Thu 09, 2004 9:59 pm 
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Chuck Schwark wrote:
<font>quote:</font><HR>Originally posted by Norm Leal:<BR><B>... If you are not familar with the smell wire a selenium rectifier in series with a 100 watt bulb to the AC line. It will burn....<P></B><HR>
<P>Smells kinda like a burning cat... <B><I>very</I></B> distinctive odor. Once smelled, never forgotten.<P><P>------------------<BR>Chuck Schwark<BR><B><I>The Philco Repair Bench</I></B> at<BR> <BR><A HREF="http://www.philcorepairbench.com" TARGET=_blank>http://www.philcorepairbench.com</A>


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 Post subject: Killer Seleniums
PostPosted: Dec Thu 09, 2004 10:36 pm 
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Location: Pocasset, Cape Cod, MA
It's been covered before. Most of my information comes from a 1970s book "Selenium" by Zingaro and Cooper, which has a chapter on the toxicology, and the series of books "Dangerous Properties of Industrial Materials" by Sax. I consider those reliable reference sources, as opposed to anecdotes heard on the internet. They both have lots of further references. Also, it's hydrogen selenide, not selenium dioxide.<P>------------------<BR>


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 Post subject: Killer Seleniums
PostPosted: Dec Fri 10, 2004 12:20 am 
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Location: Mpls, Minnesota
easyrider8 wrote:
<font>quote:</font><HR>Originally posted by Alan Douglas:<BR><B>It's been covered before. Most of my information comes from a 1970s book "Selenium" by Zingaro and Cooper, which has a chapter on the toxicology, and the series of books "Dangerous Properties of Industrial Materials" by Sax. I consider those reliable reference sources, as opposed to anecdotes heard on the internet. They both have lots of further references. Also, it's hydrogen selenide, not selenium dioxide.<P></B><HR>
<P>From the information I have been able to find Hydrogen Selenide is used in or part of the manufacturing process, Selenium Dioxide is released when it it burned.<P>The books you quote as being "reliable reference sources" are in excess of thirty years old and would not be very reliable in todays world of technology.<P>Getting back to my original question, I had asked for information concerning the dangers of using selenium rectifiers and why they should be replaced. nobody has been able to produce anything. <P>Dave<BR><P>------------------<BR>Intelligence is the ability to use your knowledge


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 Post subject: Killer Seleniums
PostPosted: Dec Fri 10, 2004 12:47 am 
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Here's the full entry for hydrogen selenide (which is produced by reaction of selenium with organic materials, or by direct combination of the elements):<P>THR [Toxic Hazard Review]:<BR>VERY HIGH irr to skn, eyes and mu mem and via inhal route. An allergen. This material is a hazardous compound of selenium which can cause damage to the lungs and liver as well as conjunctivitis. It has been found that repeated 8 hr exposures to conc of 0.3 ppm prove fatal to guinea pigs by causing a pneumonitis, as well as injury to the liver and spleen. Conc of 0.3 ppm are readily detected by odor, but there is no noticeable irr effect at that level. Conc of 1.5 ppm or higher are strongly irr to the eyes and nasal passages.<P>As in the case of hydrogen sulfide, the odor of hydrogen selenide in concentrations below 1 ppm dissappears rapidly because of olfactory fatigue. Although the odor and irr effects are both useful to an experienced investigator for estimating the conc, they do not offer a dependable warning to workmen who may be exposed to gradually increasing amounts and therefore become used to it. Due to its extreme toxicity and irr effects, it seldom is allowed to reach a conc in which it is flam in air.<P>Very little data are available on possible chronic effects of this material, but it is logical to assume that when the conc of this gas is low enough to avoid the irr effects, only the systemic effects will be noticeable.<P>Sax, "Dangerous Properties of Industrial Materials, 6th ed., 1984, Van Nostrand Reinhold.<P>------------------<BR>


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 Post subject: Killer Seleniums
PostPosted: Dec Fri 10, 2004 1:33 am 
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Location: Mpls, Minnesota
Actually I an well aware of the hazards of the misuse of Selenium. We are not talking about grinding it up and ingesting it or frying seleniums on the campfire and sniffing the smoke. We are talking about the proper use of a selenium rectifier.<P>My question has been evaded and I will pose it again. Is there any reason which can be based on fact that selenium rectifers should be replaced in a radio. <P>This could be an enlightening and informative post if we could get some factual information.<P>Dave<P><P>------------------<BR>Intelligence is the ability to use your knowledge


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 Post subject: Killer Seleniums
PostPosted: Dec Fri 10, 2004 2:07 am 
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IMO, if the selenium rectifier gets too leaky (due to age/time/stress factors) and puts too much AC on the first filter cap, the cap will eventually fail, causing resulting cascade of well known problems.<P>------------------<BR>Chuck Schwark<BR><B><I>The Philco Repair Bench</I></B> at<BR> <BR><A HREF="http://www.philcorepairbench.com" TARGET=_blank>http://www.philcorepairbench.com</A>


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 Post subject: Killer Seleniums
PostPosted: Dec Fri 10, 2004 2:08 am 
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They fail, often enough that many people here have seen them fail, and when they fail they emit a toxic gas.<P>Now that I'm at home and have Zingaro and Cooper's book at hand, here are a few quotes from the "Hydrogen Selenide" subsection of the Toxicology chapter. Incidentally, this book ("Selenium", Van Nostrand Reinhold 1974) totals 835 pages, of which the Toxicology chapter occupies 20, with 67 literature references.<P>"Hydrogen selenide is one of the most toxic and irritating selenium compounds. Gaseous hydrogen selenide is formed by the action of acids and in some cases water on inorganic selenides such as aluminum selenide. It can also be formed by the reaction of selenium with organic matter and by the direct combination of the elements.<P>(six paragraphs detailing some cases, and symptoms)<P>...Since hydrogen selenide can be produced readily and is highly toxic, considerable care should be exercised in all situations where the gas may be encountered."<P>According to the pages on selenium rectifiers, they are formed on aluminum plates with a cadmium counterelectrode, and cadmium selenide and nickel selenide are part of the process. So there are plenty of inorganic selenides present.<P>------------------<BR>


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 Post subject: Killer Seleniums
PostPosted: Dec Fri 10, 2004 4:54 am 
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Location: Mpls, Minnesota
easyrider8 wrote:
<font>quote:</font><HR><B>Originally posted by Ted:<P> <BR>That's most likely why se rectifiers are generally replaced on sight in classic radios.<P>Radios were often played right up until the time they failed, se rectifiers in particular will not tolerate heavy current draw. "Leaky" filters are the norm, not the exception.<P></B><HR>
<P>1. My Classic radios still have the seleniums<P>2. Selenium will tolerate a heavy current draw better than silicon, they are still used for welders and plating.<P>3. Electrolytics will usually open with age as the gel dries out, causing the hum we associate with failed filters. Capacitor will become leaky.<P>Dave<P><P>------------------<BR>Intelligence is the ability to use your knowledge


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 Post subject: Killer Seleniums
PostPosted: Dec Fri 10, 2004 5:24 am 
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Location: Vieques, PR, USA
Most sets will tolerate a 10 or 20 volt drop in B+ voltage with no sweat. Even 120 volt B+ sets. So the 'leaky' rectifier is often considered good because the set still 'works'.<P>Actually its quite the opposite. If its dropping excessively then its going to heat up and so on. How many times have you heard the suggestion that when replacing a Se rectifier with an Si that you need to add resistance? The voltage drop difference between the two shouldn't be more than 5 volts or so. (Depends on the number of Se sections, of course. I think we decided about 0.9v drop per section)<P>As for current capacity...aren't the ones typically found in old consumer radios only rated at about 100-150ma?<P>Me personally? I don't like to leave old partially-deteriorated components in a refurbed set...'working' or not. Its the same argument as with paper caps or dried out grommets. Might be leaky but at such-n-such point in the circuit the leakage doesn't matter. Well, thats all true but if it has started down the pike of deterioration its simply a matter of time before it craps out completely and some components have a well-deserved reputation for doing so.<P>------------------<BR>


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 Post subject: Killer Seleniums
PostPosted: Dec Fri 10, 2004 6:21 am 
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Location: Sarasota FL USA
Selenium rectifiers are notorious for causing problems that do not show up on the bench, but only in the customer's house.<P>A frequent complaint would be "I changed the 12be6, or 1R5 in the case of an ac-dc-battery set, and it played for a while but stopped again. Or the set plays on the bench but not for the customer. The selenium would develop a high forward resistance and drop the B+ to the point where the oscillator would not oscillate. A new oscillator tube would have a bit more gain and play for a while.<P>Radios with selenium rectifiers were always tested with a variac at reduced line voltage. If the oscillator cut out before getting down to 90 vac input, the selenium would be replaced. Remember that this was on radios that might be only 5 years old.<P>It was extremely rare to see a selenium burn up in a radio, but very common in TV sets. In a radio, the only time that I have seen one heat to the point of smelling, was when there was a bad short in the B+.<P>German seleniums stand up much better than American ones in radios.<P>When we first started replacing seleniums with silicon rectifiers, Silicon rectifiers were probably twice as expensive as seleniums.<P>Elemental Selenium, while toxic in larger doses, is an essential nutrient. I think that the environmental hazard from disposing of the occasional selenium rectifier in the waste stream is non-existant and its escape into the earth or groundwater would have more beneficial than harmful effects.<P>Selenium is also used in dandruff control shampoos and treatments.<P>I have been in the same room with burning or overheated seleniums and do not wish to experience it again.<P>------------------<BR>Brian McAllister<BR>Sarasota FL<BR> <A HREF="http://oldtech.net" TARGET=_blank>http://oldtech.net</A><BR>bkm@oldtech.net


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 Post subject: Killer Seleniums
PostPosted: Dec Fri 10, 2004 7:06 am 
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Here's the real reason to avoid selenium rectifiers : ) :<BR> <A HREF="http://antiqueradio.org/tvshow.htm" TARGET=_blank>http://antiqueradio.org/tvshow.htm</A> <P>------------------<BR>


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 Post subject: Killer Seleniums
PostPosted: Dec Fri 10, 2004 11:17 am 
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Location: Mpls, Minnesota
Aside from Alans hazmat information which proves nothing (like I said previously, we are not eating or sniffing burnt seleniums) there has been no documented proof that seleniums cannot be safely used in radios.<P>Now lets throw another fallacy in the garbage can, and see if it goes clunk.<P>------------------<BR>Intelligence is the ability to use your knowledge


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 Post subject: Killer Seleniums
PostPosted: Dec Fri 10, 2004 9:20 pm 
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Speaking strictly from a performance standpoint, replacing se with silicon (much lower voltage drop) will 'wake up' an otherwise dog AA5 radio, as long as your B+ does not exceed any component specs. <P>You have to admit, the silicon is much more reliable today.<P>------------------<BR>


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