What is wrong with selenium rectifiers in old tube equipment?

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Zap boosting antique tubes is such a bad idea.

Seleniums go high R with age, resulting in overheating and a severe stink. Some from the 50s still work, but a lot dont. If you need to replace one with silicon, don't completely ignore the normal selenium resistance's effect on the circuit.

NT

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The fumes are toxic too!

Silicon has a much safer 'magic smoke' inside :^)

George H.

Some from the 50s still work, but a lot dont. If you need to

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.

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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.

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

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?".

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

Thanks

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

Here's a generality article...

and more...

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I guess googles suggesting is a good start ;)

-Lasse

Cumulative toxin, stays trapped inside you forever.

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

I still have an unused 1005A laying around ;)

Cheers

Thanks for the articles.

How do you use them as photocells???

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 :-) ...Jim Thompson

I don't think so. I know the fumes are nasty as I found as a kid when I=20 overloaded a DC power pack for my electric trains and I tossed it = outside=20 and closed the door. But Selenium is a vital trace element, and AFAIK it = is=20 metabolized by the body and eventually is gone unless replenished by = chronic=20 exposure. Maybe some forms are more inert, but then why would they be = toxic?

It seems to be mostly an irritant, where high temperatures produce = Selenium=20 Hexafluoride which upon contact with moisture (as in the lungs) = decomposes=20 to elemental Selenium and Hydrofluoric Acid, which is extremely = powerful.

You may be thinking of Mercury or Lead.

Paul=20

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).
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.

There is a DC circuit breaker test set that used Selenium rectifiers for = up=20 to 30,000 amps. They were an assembly about 2 ft cube, with a powerful = (and=20 noisy) fan to keep them cool:

There is at least one company that still makes them:

Now we replace them with silicon modules:

I remember the zapper which could rejuvenate CRTs for a while, but my = father=20 and I sometimes took picture tubes to our local=20

Paul=20

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)