Just my two cents.
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I have many a power device with direct and indirectly
heated filaments/cathodes, in applications at my work,
where the typical hours of the device service life are
metered and logged.
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I would often see just about the mfgrs rated life span in
applications where filament power (well regulated)
remained on constant. Replacement of these devices
are most often done when emission drops below usable
values.
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The same type of application where the power was
shut off, then reapplied for each machine use reached
similar emission life span numbers, but there was a
very significant increase seen in filament failures.
My personal equipment log shows that value to be in
excess of 30%
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Comments made by Mauri I4JMY in a 12/31/00 post
hit home with my personal conclusions. I've come up
with my own fix.
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I have installed filament "trickle current circuits" in
some of my applications. It amounts to a relative
trickle current-to-rated filament power applied
all the time. Filament ramp up circuits are also
installed in my/our very large applications. I would
like to write that I've arrived at some rule of thumb
formula for all circuits, but life is just not that
simple.
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The end results have been very encouraging. Time
and the log books will tell. The preliminary results
are almost no lost filaments before the device
emission drops.
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Another side bar are the very interesting Semens
series lead installed hour meters installed in some
of these costly new/replacement devices I/we
purchase.
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Almost all the exact filament on time is shown on a
really cool slide display that looks like a thermometer.
As far as I know, the display cannot be reset.
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cheers
skipp
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nospam4me@juno.com
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