N4ZR says:
>For what it's worth (maybe not much) I find myself thinking about the
>relatively limited total lifetime of my 3-500 filaments, and like being
>able to leave them off altogether till I need them.
My experience (FWIW) is that there's no problem with filaments going open
from being left on: I use 4-250As, which have a filament structure pretty
similar to the 3-500, and always run them whenever on the air. This is
because my antenn relays are energise to receive; this is purposely done so
that when switched off, any lightning induced EMP goes to the tube plates
rather than the FET RF amp. So I have many hours of filament running to the
credit of the 4-250As.
But the biggest likely filament killer is if you don't have surge protection
for those filaments: the anything up tp 10 times normal current when you
switch on is likely to kill them if you repeatedly do it. Of course, if you
have a suitable filament xfmr with high leakage reactance, or
thermistors........but how many amps do have? Once you do that, the 'instant
on' could be a bit longer than you imagine. So switching the amp on for the
DX and then off, and then on for the next bit of DX.............
As far as the heat is concerned, you need less for the cathodes.......a pair
of 3-500s needs 141 watts; a 4CX1000 needs 54 watts.
And to add something to think about, a man sitting down thinking dissipates
about 150 watts.............a politician dissipates zero because he doesn't
think...
Finally, since when was anything that could be dignified by the name of beer
need to be served cold?
73
Peter G3RZP
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