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filament life Re: Max anode voltage?

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 04:03 PM 5/17/2006, you wrote:
Original poster: David Speck <Dave@xxxxxxxxxxxxxxxx>


If tubes are anything like light bulbs, you may take a significant hit on filament longevity by running them at 10% overvoltage. I read somewhere that the life of an incandescent lamp varies as the inverse cube of the current, so that works out to about 75% of the rated lifetime.

for incandescent bulbs, life goes as 1/(v^12), as I recall (although wikipedia shows 1/(V^16)

Yep, it's pretty severe.. but that's why 130V bulbs last almost forever on 110V, if they are a bit yellow, and why photofloods (which run hotter than normal bulbs, so the color temp is bluer) have 6hr rated life. (This doesn't apply to halogen bulbs)

Here's a handy app note:

the graph at the end shows 10% overvoltage gives you 30% of the nominal life. 20% Over voltage is 10% life.