Thread: Nernst Lamps
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Old 28th Jul 2021, 4:51 am   #7
TonyDuell
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Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,191
Default Re: Nernst Lamps

I once repaired an infra-red spectrometer where the light source was a Nernst glower. The advantage in that application was that the glowing bit didn't have be inside an (evacuated) glass bulb. so there was nothing to absorb the infra-red radiation.

The ballast was a box containing officially 3 0.3A barretter lamps with switches to select 0.3A and 0.6A, both on giving 0.9A of course. When the bulbs failed we fitted normal 60W bulbs which seemed to work.

Anyway, the startup procedure was interesting. There was no heater coil on the Nernst element. Instead you opened up the lamphouse, took a screwdriver, put bit of cotton wool on the end, soaked it in ethanol and lit it. Then used that to heat the Nernst element. When it started to glow you removed the screwdriver and closed the lamphouse. Remember that the Nernst element was connected to the mains...

I don't know the date of the instrument, but it can't have been all that old (1960s?) The amplifier unit was mostly valved, but there was an OC-something-or-other transistor in there too.
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