John T. M. Lyles wrote:
>
> I have never heard that story that running filaments alone without HV
> will shorten emission life.
I would love to hear the theory behind that and
> some more examples besides the RF heating app you quoted. Unless they
> had the filament set too high. If the tubes are not drawing current,
> (anode) then they should be backed off on filament to get even longer
> life during this time. Thales and other tube companies call this
> "dark heat" standby mode.
John and all,
I wish I could provide more background. It's been a lot of years and at
the time I was still in my "cowboy" era where I only cared about how
much power I could squeeze out of a tube no matter how much damage I
caused it. I just knew I could get power out of those tubes where the
factory rep could not in his equipment. I kinda disregarded most of what
I was told at the time. I could have some of the details wrong, but I am
very sure the factory rep said the reason for the very low emission was
due to running the filaments permanently on and cycling the RF power for
a few seconds every now and then. Perhaps even a month or so between
cycles from what little info I had. The tubes were definitely 3CX1000's.
Also I know I have seen documentation at some time years ago which
cautioned against this type of operation but I cannot remember the
context or the tubes involved. I am pretty sure it was thoriated
tungsten types but after all this time, I can't be positive. If I run
across the info, I'll be sure to post it here.
73,
Larry - W7IUV
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