To answer your question. NO, DON'T Worry about it. This myth really
got rolling with the introduction of high pressure Quartz Halogen lamps.
These lamps have very very hot filaments with high pressure inside (which
increases with temperature) and the hot gas is in contact with the
envelope. They are delicate and if certain contaminates get on the surface
the surface of the quartz envelope can be damaged either by etching
(quartz is very difficult to etch) or by causing a hot spot. Another
source of the myth could have been the photography enthusiasts. They always
cautioned people about finger prints on lens because they may etch into the
optical glass. However, it is likely that the coatings would be damaged
first before even the oils even got to the glass. Go to the kitchen and
look at all the glasses that you have put away months or years ago that you
have not moved. They should have finger prints on them. Are they etched
into the glass? Do they come off in the dish washer? If they did etch
into the glass you would see all sorts of product advertisements stating
that their dishwasher liquid or what ever prevents the problem.
Also, if glass were so easy to etch then it would not be used for
chemistry test tubes. Etching would contaminate the contents of the the
test tube.
Saying that, I will say that it is good to keep the envelopes of the
tubes clean , but perfection is not necessary, white silk gloves are not
necessary. Finger prints will not kill your tubes. Relax.
A 3-500Z or even bigger tubes anodes get red hot at times but much
lower temperature than the Quartz Halogen lamps filaments. Also, the only
thing heating the envelop radiant heat, most of which passes straight thru.
I have yet to see a power tube envelop burst due to some contaminate
on the surface of the envelope. I guess if someone really worked at it they
could damage do it. But the anode would have to get quite a bit hotter than
the melting point of glass to damage the glass by radiated heat. The seals
would probably go first. They are the weak parts of the envelope. Heat is
conducted by the metal to the seals where there may be a very slight
difference expansion rate due to temperature. This can put stress in the
areas where glass meets metal and create a crack. This then allows air to
enter the tube. That is why it is important to cool the base (pin seals)
and plate caps (anode seals) of the tubes.
73
Bill wa4lav
At 10:45 PM 2/28/2005 +0100, Geert Jan de Groot wrote:
>Should I worry about not getting fingerprints on the glass of glass-enclosure
>tubes like the 3Z500?
>
>Should this have happened, what would be the best way to wipe them?
>
>Geert Jan
>_______________________________________________
>Amps mailing list
>Amps@contesting.com
>http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|