[Amps] A Filament Query

[Roger (Sub1)]

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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