Lightbulb Filament Replacement

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harry wrote:

Some light bulbs do have a vacuum, including most 120V ones 15 watts and less, as well as 120V tubular showcase/refrigerator lamps up to 40 watts, and many others with design current near or under .2 amp.
If the filament is thinner, then the temperature gradient in the gas around the filament is greater, and heat conduction loss by the gas per unit filament area is greater. At some point, it gets better to use a vacuum and run the filament at a lower temperature than it is to use the usual argon-nitrogen mixture. At some further point of decreasing filament diameter, it gets better to use a vacuum than it is to use even premium fill gases such as krypton or xenon.
Incandescents with a vacuum tend to have yellower light and cooler surfaces than gas filled ones of similar wattage.
--
- Don Klipstein ( snipped-for-privacy@misty.com)

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On 9/14/2010 9:50 AM, Don Klipstein wrote:

The way I read this is that the filament's heat losses are all radiative in the vacuum case. The reason it runs at a lower temperature is because it is longer, otherwise it should be hotter for the same power out as it's not dissipating heat as fast.
What did I get wrong?
Jeff
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wrote:

Standard light bulbs are not a vacuum, they are filled with argon.
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Most are indeed filled with a gas, usually an argon-nitrogen mixture, maybe 93% argon 7% nitrogen.
But if the ratio of power input to visibly apparent filament length (that is, before uncoiling it) is less than something like 20 watts per inch or so, then the bulb usually has a vacuum rather than gas. Only when the ratio of power to filament length is above somewhere around there does the benefit evaporation retardation of the gas (allowing higher filament temperature) outweigh the heat conduction loss caused by the gas.
One way to tell if a light bulb has a gas fill or a vacuum is to see if the top of the bulb gets very hot (that means gas). If you have a Tesla coil handy, it gets easy to tell - bulbs filled with the usual argon-nitrogen mixture will have pink streamers form in them (sometimes with violet areas at their ends) if they are brought close to a running Tesla coil. Vacuum ones generally refuse to glow, but could develop a somewhat uniform glow over their inner surfaces from extreme slight trace of some gas with enough voltage from a Tesla coil. (Don't do that for long - possible X-ray risk.)
I know this from experience.
--
- Don Klipstein ( snipped-for-privacy@misty.com)

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On Tue, 14 Sep 2010 21:29:49 +0000 (UTC), snipped-for-privacy@manx.misty.com (Don Klipstein) wrote:

Just thinking of the term "Vacuum Tube" like the old tv and radio tubes. I would assume they had a vacuum. They also had a filament similar to a light bulb, but lower voltage and they never clowed more than a dull orange. which would tell me that they are running at a low current draw. I recall testing them in the old days and there was a test for "Gassy". I believe that meant that air had leaked in, because I sure cant see how they could have gotten any actual gasses in them. I remember taking old tubes that were bad but still had a working filament and over voltaging the filament. It really did produce light for a short time. Like running 12V into a 6V tube. I also liked to watch the bluish glow in the old power tubes, like the finals in audio amplifiers. It moved to the music, which was actually the power loads inflicted on the tube by mostly the bass.
Sorry, if you're under 35 or 40, you probably have no clue what I'm talking about. :) It's just electronic history..... Google "Vacuum Tube". They were pretty neat things. I liked playing with the old tube stuff when I was a kid, even if I did get knocked on my ass a few times, because those circuits often had 300 to 1000 Volts DC, and that can knock you down real fast. And worse yet were those old TV CRTs that held a charge for hours after being turned off.
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On 9/15/2010 2:32 AM, snipped-for-privacy@myplace.com wrote:

Back in the heyday of CB radio, I had a 500watt Phantom linear amp hooked to my Avati Astro Plane antenna and I was on a hill. My bud who was listening in his vehicle down in the swamp 50 miles away, said I pegged his S meter. The output tubes of that big old amp were glowing bright blue and the sparks were dancing to my voice. I worked on color TV's that had a round face picture tube and chassis that weighed in at 100lbs. You could heat a house in winter with some of that old tube gear. 8-)
TDD
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On 9/15/2010 3:32 AM, snipped-for-privacy@myplace.com wrote:

Just yesterday I "rebuilt" a tube amp for an old juke box. All new caps, 10 or so resistors, and 6 new tubes. This one has some odd ball output tubes and it took all 4 (push pull stereo) (grid leakage). 6L6's are usually good for the "blue light show".
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wrote:

Yep, 6L6's were some of the most used tubes of all in the old tube amps. I used to have two matched and modified guitar amplifiers hooked to my stereo. Each amp has 4 6L6s in push pull parallel. Those 6L6s really did get a good glow. Particularly the older ones that were shaped sort of like lightbulbs (fat in the middle). The newer ones that were straight on the sides were not quite a vivid, but still did ok.
I wonder what tubes you got in that old amp? I recall some really old tubes which if I recall, were 807s (something like that). I also had another real old amp that had a voltage limiting tube or was that current limiting? They glowed purple. Gees, that's a long time ago, I'm starting to forget all those tube numbers. I do recall the 12AX7 and 12AU7 were often used as preamps, and 5U4 rectifiers.
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wrote:

Well, I'm just slightly under 60 years old. Yes, I remember where most tubes would turn white if they got a little crack in them. I never knew why. Thanks for that info.
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I think you got it right - in vacuum incandescents, they make the filament longer than if gas was used so that the filament would run cooler.
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On 9/14/10 10:58 AM, Jeff Thies wrote:

The temperature also depends on input power. The ambiguous area is between 6 and 10 watts per cm of filament.
Gas allows a filament to run hotter, which is more efficient. If you aren't going to run the filament that hot, vacuum is more efficient.
I have Westinghouse's Large Lamp Specification Guide from 1975. Most bulbs of 50 W and less were vacuum. 60 and 75W were a mix. Everything of 100W and up seemed to be gas.
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On Sep 15, 2:47am, snipped-for-privacy@myplace.com wrote:

Right. None of us want your vote to count.
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