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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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2nd Jun 2018, 10:46 am | #1 |
Heptode
Join Date: Apr 2010
Location: West Midlands, UK.
Posts: 662
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Nernst Filaments NFT2 and NFT4
I found three of these in a box of valves and bulbs I bought at a meeting.(2 NFT 4, 1 NFT2 ) apparently new in plastic tubes dating from the 1980's, made by the English Electric Valve Co. Looking on the net they were used in "glowers" as sources of infra-red radiation. Does anyone have any more information about them?
Mike. |
2nd Jun 2018, 11:51 am | #2 |
Dekatron
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,208
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Re: Nernst Filaments NFT2 and NFT4
I don't know about those particular filaments, but Nernst glowers were used as the infrared light source for spectrometers used for chemical analysis. The great advantage over a normal metal filament is that you can run them in air, without a glass bulb around them which might absorb some wavelengths of infrared light (In such spectrometers, reflection optics -- mirrors and reflection gratings are used wherever possible, the transmission compoennts (windows, the odd lens) on the ones I worked on were made from sodium chloride (yes, common salt) and had to be kept dry for obvious reasons).
In the instrument I remember most clearly, the Nernst glower was connected to the mains with a ballast resistor in series. This was originally 3 0.3A Barretters, with switches to select 1, 2, or 3 in parallel. When those failed, normal 60W bulbs were used, which seemed to work just as well. The glower has a negative temperature coefficient of resistnce, the resistance reduces as it gets hot, hence the need for the ballast. And also the resistance at room temperature is so high the thing will not start by itself. Posh units had a nichrome (or similar) heating element wound round the glower. But the instrument I worked on had to be started by hand. A screwdriver with a cotton wool pad on the end. Soak that in alcohol, light it, and stick it under the glower (remember, connected to the mains). After a few seconds the glower would light up (as did the ballast lamps), you took the flaming screwdriver out and put the covers on. |
2nd Jun 2018, 6:48 pm | #3 |
Heptode
Join Date: Apr 2010
Location: West Midlands, UK.
Posts: 662
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Re: Nernst Filaments NFT2 and NFT4
Thanks for the information, I don't think I will try them, the mode of operation sounds a bit scary!
Mike. |
2nd Jun 2018, 7:11 pm | #4 |
Dekatron
Join Date: Jan 2012
Location: Brentwood, Essex, UK.
Posts: 5,339
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Re: Nernst Filaments NFT2 and NFT4
Nernst lamps were produced for domestic lighting in the Edwardian era as they were more efficient than Carbon filament lamps, but were superseded by Tungsten filament lamps. Interesting to know that they continued to be manufactured into the 1980's for specialist applications.
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