Hi Denny and others,
The 60 hour loss of life for each off/on cycle is new information for me.
What is the mechanism that drives that? Are there methods to mitigate the
effect?
This subject just begs for more discussion.
73,
Gerald K5GW
In a message dated 1/15/2011 7:22:57 A.M. Central Standard Time,
ad4hk2004@yahoo.com writes:
Roger and Carl... I'm aware of the cycling number, which is why after
mulling it over in my mind I opted to recommend the 3% drop during the idle
periods as opposed to attempting to hit the magic minimum voltage all the
time... Certainly your method works as proven by your amps... The problem I
encountered with attempting to hit the minimum filament voltage is when the
power company quietly drops the line voltage by 20 volts to save coal - and
kill my expensive tube...
A 3% decrease will double the filament life (5% will triple it)... A 3%
decrease keeps the hot oxide from passing down/up through the critical
temperature (mid 600F range) which is the major part of the loss of lifetime
of
60 hours, that each off/on cycle does to a tube... A 3% swing (and even 5%
probably) will not subject the filament to undue stress, either electrical
or mechanical as there will not be an "inrush" then the voltage is raised -
the filament is still a medium orange hot and has significant resistance at
a 3% decrease...
denny / k8do
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