Quote:
Originally Posted by BCA
Going back to the cloth socks: maybe they were to prevent finger prints contaminating the glass surface. Lighting technicians are very careful not to leave finger prints etc when changing high power light bulbs. The contamination may affect the glass. I think halogen bulbs in typical work lights are to be handled carefully too.
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You're thinking of Tungsten/Halogen (Quartz/Iodine) lamps which have an envelope of fused quartz that is badly affected by contaminants (e.g. skin oils) which absorb more heat than the rest of the envelope. The resultant hot-spot can cause the quartz to change to a crystalline form (which is much weaker) and also leak gas. (It can also weaken the envelope and cause it to shatter or explode due to the internal pressure.)
(If you get fingerprints on a Tungsten/Halogen lamp when changing it,you need to carefully clean the contamination off with an alcohol-soaked cloth before using it.)
It's very unlikely to affect vacuum tubes, even the early silica-envelope high power ones used by the Navy, as I don't think they ran nearly hot enough for that to be a problem. (Then again, it must be a couple of decades since I last looked in the Admiralty Handbook of Wireless Telegraphy!)
Best regards,
Chris.