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

"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

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