#1
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Do seleniums get weak?
Title says it all.
I've got a portable with selenium rectifiers that starts out good, and then after ten minutes, the set starts losing power, signal, deflection, etc. I know they should be replaced with some 4007's, but I want to make sure I got this power loss problem fixed first before popping in new diodes.
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Charlie Trahan He who dies with the most toys still dies. |
#2
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Seleniums get weak (increased forward voltage drop) with age. Does your symptom seem to be thermal in nature? If you use a fan or cooling spray to keep the seleniums cool, does the set work OK?
Seleniums were often used in a voltage doubler arrangement, and the 2 capacitors in the doubler can also cause problems if they get leaky or lose capacity as they warm up. Replacing both the rectifiers and the doubler caps is the real fix. |
#3
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Selenium rectifiers are a problem waiting to happen. They deteriorate with time, generally, in all aspects. The symptoms are reduced output, increased ripple, and greater heat loss as well as that characteristic odor.
Not to say that retrofitting with silicon will solve your problems, but it does eliminate one possible source. |
#4
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The set has all new capacitors, so that's ruled out. Not sure if issue is thermal... since it only takes ten minutes or less to start having problems.
I will be putting in new diodes anyway... I was just curious if these things got weak before crapping out. Thanks for your input!
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Charlie Trahan He who dies with the most toys still dies. |
#5
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Uh-oh, better not fire up anything else before replacing seleniums, you could have the smell of another rat's nest to deal with.
Man, that one will never get old, at least not to me. |
Audiokarma |
#6
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Seleniums also develop reverse leakage. This adds to the heating already caused by excessive forward drop.
Last edited by old_coot88; 10-25-2013 at 12:24 PM. Reason: Typo |
#7
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Quote:
All except Admiral and Philco. Then a few of the others went to back to 5U4"s. Then everyone but RCA, quit building color sets. |
#8
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I've heard that the mechanical connection between selenium rectifier plates through washers etc. can oxidize over time and reduce their output. Be interesting to hook a DVM to the B+ and watch the voltage from cold startup.
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Reece Perfection is hard to reach with a screwdriver. |
#9
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If it's true about corroded contacts, perhaps tightening the center bolt or even disassembling the unit and putting it back together might improve operation.
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#10
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Easier and safer to upgrade to a 1N4007 at that point....
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Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
Audiokarma |
#11
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Of course that's true, but the OP seems reluctant to modernize just yet.
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#12
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Nah man... I'm not going that route. That would be like playing with fire... not worth it. The set is getting new diodes... and probably toss in a CL-90 as well for good measure. I just wanted to know if these old rectifiers actually got weak.
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Charlie Trahan He who dies with the most toys still dies. |
#13
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We should have a cross reference from seleninum to silicon
Rectifiers with a new layout per TV set with new schematic Showing changeover to a new setup |
#14
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You'll know when a selenium goes bad. Rotten eggs, big time!
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Let me live in the house beside the road and be a friend to man. |
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