On 1/14/2011 3:42 PM, Dennis OConnor wrote:
> Here are a few references I have bookmarked in my electron tube folder...
>
> Black heat is normally ruinous to tubes - ymmv -
>
> I ruined a really nice 3CX1200 when the carefully adjusted filament voltage
> right at the lower limit of mfr's rating got further decreased by a sneaky
> power company trick of dropping their voltage a few percent during the post
> 11PM to 5AM low usage time period - when I was transmitting at full-bore,
> war-emergency power on topband...
>
> Twere me, I would lower the filament voltage at rest by 3% which gives a huge
> increase in filament life without undue risk of poisoning the oxide, and then
> pop it up to full rating for a short period, perhaps 2 seconds, before the 1
> second operation...
In this particular instance with the short on time every minute we are
looking at 1440 heating cycles per day. With that many cycles I wonder
if just leaving it alone (or running near the minimum voltage) would
give better life than cycling it 1440 times a day 10080 times a week,
40,320 times a month or 438,840 times a year.
73
Roger (K8RI)
>
> http://www.cpii.com/docs/related/22/AB18.pdf
> http://www.w8ji.com/vacuum_tubes_and_vaccum_tube_failures.htm
> http://www.archive.org/stream/VacuumTubeDesign/Rca1940VacuumTubeDesign_djvu.txt
>
> denny / k8do
>
>
>
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