What is wrong with selenium rectifiers in old tube equipment?

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In this article for antique 1955 to 57 Zenith tv set, a guy says to
replace the selenium rectifiers in the tv. What is wrong with them, or
do they go bad from age? I remember working on a lot of the old tube
stuff that had the selenium rectifiers, and I always thought they were
an improvement over tube rectifiers.

The article is here:
http://www.antiqueradios.com/forums/viewtopic.php?t=118996

One other thing. I know a guy who has one of these old Zenith sets. (a
little different than the one pictured on this site, but about the same
age). The CRT is nearly dead, you can only see the picture in a dark
room. He tested everything else, and already put on a CRT booster, so
the tube is just plain worn out. He wants to find a new CRT, but dont
know where to buy them (if they are even available). Do any of you know
of a place that still sells replacments? I also recall hearing (years
ago), that there is (was) a company that rebuilt CRTs. Anyone know
anything about any of this?

Thanks

 

[Tauno Voipio]

In this article for antique 1955 to 57 Zenith tv set, a guy says to
replace the selenium rectifiers in the tv. What is wrong with them, or
do they go bad from age? I remember working on a lot of the old tube
stuff that had the selenium rectifiers, and I always thought they were
an improvement over tube rectifiers.

The article is here:
http://www.antiqueradios.com/forums/viewtopic.php?t=118996

One other thing. I know a guy who has one of these old Zenith sets. (a
little different than the one pictured on this site, but about the same
age). The CRT is nearly dead, you can only see the picture in a dark
room. He tested everything else, and already put on a CRT booster, so
the tube is just plain worn out. He wants to find a new CRT, but dont
know where to buy them (if they are even available). Do any of you know
of a place that still sells replacments? I also recall hearing (years
ago), that there is (was) a company that rebuilt CRTs. Anyone know
anything about any of this?

Thanks

Ever burned one? The stink is undescribable and poisonous.

The recommendation is to take a bunch of 1N4007's and replace
the seleniums with them.

 

[Tauno Voipio]

I think adding some resistance in series with the diode would be
good idea, so that it behaves a bit more like what it should replace

-Lasse

That's right.

I should have told it, as I have an experience, about 40 years ago:

My friend had an old Telequipment oscilloscope with badly soft picture,
because the high voltage was far below the specified 750 V. The cuprit
was the tube diode rectifying the voltage, so he replaced it with a
couple of 1N4007's (with equalising resistors and caps). The voltage
came immediately up to the specified 750 V, with a brilliant picture.
After a few minutes, there was a pfffft sound, and quickly the air got
filled with confetti, as the filter capacitors did not stand the full
voltage anymore.

 

[Don Lancaster]

Ever burned one? The stink is undescribable and poisonous.

The recommendation is to take a bunch of 1N4007's and replace
the seleniums with them.

My first real job involved being a helper in making tv repair house calls.

The first thing that nearly always got asked was "Maam, have you been
cooking cabbage?".



--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

[[email protected]]

All of them (including new ones) that I ever scoped had a lot of
reverse leakage. I will repeat: If you replace with a silicon diode
the voltage will be a lot higher unless you do something about it!
John Ferrell W8CCW

So what would be something close to the necessary resistance required to
compensate for the selenium rectifiers, when replaced with modern
silicone diodes?

Thanks

 

[Martin Riddle]

Here's a generality article...

http://www.w3hwj.com/index_files/RBSelenium2.pdf

and more...

http://wiki.answers.com/Q/Can_you_replace_a_selenium_rectifier_with_a_silicon_rectifier

...Jim Thompson

I still have an unused 1005A laying around

Cheers

 

[[email protected]]

Years ago I recall an article for making a Selenium replacement. I'll
see if I can find it.

I had tons of those available to me in my Dad's TV repair shop. I
used to dismantle and use them as photocells.

...Jim Thompson

Thanks for the articles.

How do you use them as photocells???

 

[P E Schoen]

"Father Haskell" wrote in message

Cumulative toxin, stays trapped inside you forever.

I don't think so. I know the fumes are nasty as I found as a kid when I
overloaded a DC power pack for my electric trains and I tossed it outside
and closed the door. But Selenium is a vital trace element, and AFAIK it is
metabolized by the body and eventually is gone unless replenished by chronic
exposure. Maybe some forms are more inert, but then why would they be toxic?
http://en.wikipedia.org/wiki/Selenium_poisoning#Toxicity

It seems to be mostly an irritant, where high temperatures produce Selenium
Hexafluoride which upon contact with moisture (as in the lungs) decomposes
to elemental Selenium and Hydrofluoric Acid, which is extremely powerful.
http://www.atsdr.cdc.gov/mmg/mmg.asp?id=1015&tid=215

You may be thinking of Mercury or Lead.

Paul

 

[P E Schoen]

"Robert Baer" wrote in message

1. Selenium rectifiers were better due to lower forward drop, but
were a potential killer (literally) if abused (think circuit fault
causing over-voltage and/or over-current).

There is a DC circuit breaker test set that used Selenium rectifiers for up
to 30,000 amps. They were an assembly about 2 ft cube, with a powerful (and
noisy) fan to keep them cool:
http://www.hccontrol.co.za/Search/Suppliers/Megger/cb/Datasheets/CB360_DC_DS_en_V10.pdf

There is at least one company that still makes them:
http://superior-power-components.com/Selenium rectifier introduction.html

Now we replace them with silicon modules:

2. Many years ago, a number of US CRT makers would also re-build
them. Then making them got off-shored, then the re-building also
got off-shored and all the makers in the US closed shop (for CRTs)
and the re-building seems to have stopped then.

The Zenith is good only for museums.

I remember the zapper which could rejuvenate CRTs for a while, but my father
and I sometimes took picture tubes to our local
http://www.baynesvilleelectronics.com/index2.ivnu to be rebuilt or in trade
for rejuvenated ones at a significant cost saving.

Paul

 

[Adrian Tuddenham]

"Father Haskell" wrote in message



I don't think so. I know the fumes are nasty as I found as a kid when I
overloaded a DC power pack for my electric trains and I tossed it outside
and closed the door. But Selenium is a vital trace element, and AFAIK it is
metabolized by the body and eventually is gone unless replenished by chronic
exposure. ...

Selenium Sulphide was used in anti-dandruff hair shampoos. There was a
warning not to apply it to damaged skin, but nothing about cumulative
toxicity.

(The shampoo smells quite similar to burnt-out selenium rectifiers)

 

[[email protected]]

Selenium Sulphide was used in anti-dandruff hair shampoos. There was a
warning not to apply it to damaged skin, but nothing about cumulative
toxicity.

(The shampoo smells quite similar to burnt-out selenium rectifiers)

I questioned this too, knowing that every so many years (I think they
say about 7 years), every cell in a human's body is replaced. So
without repeated exposure, it would diminish, and eventually be gone.

In addition, Selenium is actually required by the human body in small
amounts. Animals particularly livestock need higher amounts. Of course
this needs to be ingested, not inhaled from being burned.

Of all the old electronic gear I worked on when I was much younger, I
never had a selenium rectifier burn up. I probably still have a dozen
or so of them in my old parts boxes. I used to save all that stuff, as
long as it was still in good shape.

 

[[email protected]]

I retained the clips that made contact to the faces, and used a Nylon
screw. They are a giant photodiode. I only used them in photovoltaic
mode... I was like 14 at the time, didn't know any other way

I was just reading that selenium is used in photocells. I never knew
that. This brings up another question. If they are a photodiode, what
effect does exposing a working selenium rectifier to light have? In
other words, if I have an old radio with selenium rectifier inside a
cabinet, when I pull the chassis out of the cabinet for repair, that
rectifier will be exposed to light, and normally bright light, because
my work bench is always well lit. What effect will the light have on
the output voltage after the rectifier, V/S the same rectifier inside a
dark cabinet?

I did most of my puttering with electronics when I was in my teens. By
the time I was 20, I was more interested in women and booze. By the
time I was 30, the electronics were more interesting again

 

[Fred Abse]

I was just reading that selenium is used in photocells. I never knew
that.

And photocopiers, and laser printers.

 

[[email protected]]

I questioned this too, knowing that every so many years (I think they
say about 7 years), every cell in a human's body is replaced. So
without repeated exposure, it would diminish, and eventually be gone.

That's an old wives tale. Skin cells are replaced regularly, as are a few
organs, but muscle and nerves are forever.

In addition, Selenium is actually required by the human body in small
amounts. Animals particularly livestock need higher amounts. Of course
this needs to be ingested, not inhaled from being burned.

Of all the old electronic gear I worked on when I was much younger, I
never had a selenium rectifier burn up. I probably still have a dozen
or so of them in my old parts boxes. I used to save all that stuff, as
long as it was still in good shape.

I burned up a pile of them when I was a kid. I used to save all that stuff,
too, until I moved a few times. I cart around enough stuff that I use. The
useless stuff gets pruned quickly.

 

[[email protected]]

I was just reading that selenium is used in photocells. I never knew
that. This brings up another question. If they are a photodiode, what
effect does exposing a working selenium rectifier to light have? In
other words, if I have an old radio with selenium rectifier inside a
cabinet, when I pull the chassis out of the cabinet for repair, that
rectifier will be exposed to light, and normally bright light, because
my work bench is always well lit. What effect will the light have on
the output voltage after the rectifier, V/S the same rectifier inside a
dark cabinet?

Sure, selenium is used in the better photographic light meters. BTW, silicon
is photo-sensitive, too. What happens when you put your TV in a dark closet?

I did most of my puttering with electronics when I was in my teens. By
the time I was 20, I was more interested in women and booze. By the
time I was 30, the electronics were more interesting again

By the time I was 20 I'd been married for two years. That left electronics
and beer. By the time I was 30, I'd been working for 10 years and had a kid.
That only left time for electronics. ;-)