On Thu, 30 Apr 1998 09:20:42 +0100 Peter Chadwick
<Peter_Chadwick@mitel.com> writes:
>Been out a couple of days.
Me too Peter.
>
>Spectrum analysers - can lie worse than a Personnel manager, even more
>so
>with a FET probe.
>
>Thoriated filaments. Rich is quite right about the carburization
>business -
>it's described in old editions of Terman. However, leading on from
>that, the
>maximum emission when saturated from a 3-500Z filament (or any of the
>5volt,
>14.5Amp thoriated filaments is of the order of 60 to 70mA/watt. That
>means
>a maximum tube current, in saturation, as opposed to arc current, of
>around
>4 to 5 amps dc.
And the DC arc current can be over 100A depending upon the PS and
suppressor.
If that is going to bend filaments, why is there no
>warning
>about running the filaments on dc? And will the grid bend at 5 amps?
I asked at least one "expert" to do the math to prove it and got nothing
back but a vacuum.
>Maybe
>someone can calculate the bending force. If that current is the result
>of a
>parasitic, where does the plate get its current from?
If it was a parasitic then the tube is in an amplifying or oscillating
state.....correct?
In the case of a runaway parasitic then would you not expect to see the
plate current soar and the plates glow white? This takes a finite amount
of time to occur and if not quickly stopped will result in a failed tube.
However a gas arc is an instantaneous occurance and will not act as
above.
>
>This is why I have a problem with the parasitic theory.
As do most people that bother to examine the process instead of asking
pointless questions or suggesting even more after the fact meaningless
tests.
73 Carl KM1H
>
>73
>
>Peter G3RZP
>
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