Re: Selenium rectifiers in Tek equipment


stevenhorii
 

Having been told for years of the hazards of lead during soldering, I
researched it a bit. As others have noted, the heat used for ordinary
soldering is not high enough to produce lead fumes - well below the boiling
point. This is just one example I found:

https://eta-safety.lbl.gov/sites/default/files/Soldering%20Guidelines.pdf

However, every reference I did find pointed out that the fluxes and rosin
used during soldering are vaporized/oxidized by the heat of soldering and
can be hazardous. Contact with lead is a problem because of inadvertent
ingestion.

My brother is an artist and would occasionally use lead-based pigments. He
used to say that there was no non-lead white paint that had quite the same
appearance as lead white when dry. He took extraordinary measures to avoid
accidental ingestion - hand washing, keeping food out of the painting area
in his studio, using separate brushes and palettes for any lead-containing
paints, and mostly avoiding lead pigments almost all the time.

Lead salts apparently have a sweet taste and is an explanation of why
children will eat lead paint chips when they peel from or fall off of
painted surfaces.

So I was incorrect - you are not more likely to be exposed to lead from
soldering as you are to selenium from bad selenium rectifiers. Selenium
dioxide does smell terrible according to the various sources I checked and
it does sublime. The supplement form of selenium is usually
selenomethianine which also smells bad. Unless you are specifically told
that you need to take a selenium supplement, I would suggest avoiding them.
There are reported cases in the medical literature of selenium poisoning
from taking too much selenium in supplements.

On Sat, Feb 6, 2021 at 04:59 Tom Gardner <tggzzz@gmail.com> wrote:

The process by which solids turn directly to vapour is called sublimation.
The
process is exactly the same as boiling: by chance a molecule is given a
sufficiently strong kick that it detaches from nearby molecules. Of course
the
chance of that happening is much lower, so the process is much slower.

The easiest place to see this is in a domestic freezer: the food gets
"freezer
burn", and the water is deposited as hoar frost elsewhere in the cabinet.

Whether that is a problem with Pb or Se is a different issue, of course.


On 06/02/21 06:53, Dave Seiter wrote:
I still don't believe melting solder produces actual Pb fumes. You
are melting it, not boiling it. Pb boils at a much higher (>5x)
temperature than it melts at. How do you get fumes below boiling
temperature? I've seen years worth of warnings, but never an explanation
of where said fumes actually come from. I'd love to be proven wrong...
-Dave

This suggests being cautious, but not obsessive-compulsive cautious. We
probably get exposed to more lead fumes from soldering than selenium from
bad rectifiers





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