If the tubes are already in the amp, leave 'em alone.
It's too easy to damage a glass to metal seal.
-SC
>
> From: Bill Fuqua <wlfuqu00@uky.edu>
> Date: 2005/03/01 Tue AM 09:09:07 EST
> To: Geert Jan de Groot <pe1hzg@xs4all.nl>, amps@contesting.com
> Subject: Re: [Amps] Fingerprints on 3Z500 tubes
>
> 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
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