[Amps] Thoriated tungsten lifetime when idling tspa

[Larry]

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