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#1
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Filament heating: constant voltage or constant current?
I finally got round to posting something I put together a while back,
analysing the merits of constant current and constant voltage filament/heater operation and their possible effect on tube longevity. It's at www.john-a-harper.com/FilamentHeating . (Makes a change to have something about tubes in this newsgroup, lately anyway!). John |
#2
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"John Harper" wrote in message
news:1082084486.105776@sj-nntpcache-3... I finally got round to posting something I put together a while back, analysing the merits of constant current and constant voltage filament/heater operation and their possible effect on tube longevity. Nice work on integrating the equations, but it says little of how a fast or slow warmup directly affects tube life, aside from your observation. Think you could maybe set up a circuit which switches the power on and off to a heater every 60 seconds then measure Gm after periods of 100 hours or so? Tim -- "I have misplaced my pants." - Homer Simpson | Electronics, - - - - - - - - - - - - - - - - - - - - - - --+ Metalcasting and Games: http://webpages.charter.net/dawill/tmoranwms |
#3
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Interesting article John: You have to be old enough to
remember the great invention called a "tube brightener" which was a step up autoformer transformer that was attached to the CRTube filament in a TV set so that the original brightness could be restored. The life span of a CRT was very short in the early days. I worked on the transformer/magnetics system for "instant-on" for color TV. The first system was a filament transformer with a "tuned choke" for a constant current circuit. Westinghouse was the tube supplier at the time. They did a great amount of the work on the system. They kept speaking of "keeping the tube current at a proper level so that the tube would stay in the desired thermeonic range." The second generation was that of an EI lamination ballast (choke) placed in series with the filament transformer. We assigned our patent rights to Magnavox since they were the end user. The good news was that the life of the CRT became significantly longer with the use of either system. The best news was that the series ballast unit only cost $1.65 in 100,000 quantities. Color TV in the earliest days. On Fri, 16 Apr 2004 01:41:28 -0500, "Tim Williams" wrote: "John Harper" wrote in message news:1082084486.105776@sj-nntpcache-3... I finally got round to posting something I put together a while back, analysing the merits of constant current and constant voltage filament/heater operation and their possible effect on tube longevity. Nice work on integrating the equations, but it says little of how a fast or slow warmup directly affects tube life, aside from your observation. Think you could maybe set up a circuit which switches the power on and off to a heater every 60 seconds then measure Gm after periods of 100 hours or so? Tim |
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