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Re: [TCML] unknown tube...



BunnyKiller wrote:
Hey Jim...

it is common belief not to touch halogen bulbs due to skin oils, it is also not good to touch hi impulse bulbs used for lasers also...but then again, both of these types of bulbs are operating in hi temperature enviroments and most are under hi pressure... 3 - 10 atmospheres.

Xenon short-arc bulbs as popular in projectors these days also fit in the category. High pressure, high temps, etc.


The
actuall arc is normally in contact with the "glass" envelope ( normally made from quartz glass, halogen having the tungsten element within millimeters of the glass) and knowing that an arc can create excessive temperatures ( whe are talking plasma temps), the oils left behind from handling can in many cases compromise the general integrity of the envelope ( causes tiny hairline fractures in the glass surface which leads to an explosive failure). As far as contaminating the envelope of a vacuum tube device, you must ask the question of does it lend itself to the same heat levels as an arc lamp? Is an arc being formed and is it in close proximity to the envelope? With what I do know of vaccum tube devices, I would have to say that touching the outer envelope would not be detrimental to its life as it would be for say a laser style discharge lamp... Im old enough to remember the TV repair man coming to the house to replace tubes in the TV and he never cleaned the tubes he handled when he replaced them.... and they would glow red when the TV was on... damn Im old....someone would actually come to the house to fix the TV!!!


I think you're right. On the run of the mill receiving and low power transmitting tubes, I can't see a finger print making much difference. Heck, even if the plates are running orange, it's no where near as hot as any sort of "lamp".

OTOH, tubes typically have envelopes made of glass, as opposed to silica, so the thermal stresses are much greater (glass has a much higher CTE than silica). Might be that fingerprints on glass at 1000C are as big a problem as fingerprints on silica at 2000C..





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