I have just spent an entire semester working on electro magnetism and the
physics is VERY fresh in my mind. Eric's calculations are sound, I am sorry
Rich but you are way off the mark here, there is no way that sufficient
magnetic flux could have been generated in the scenario you describe.
Certainly nowhere near enough to distort the grid wires as you have
suggested.
I suggest that you re-think this one. I can quote some equations at you if
you wish.
Regards
Conrad G0RUZ
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]On
Behalf Of Ian White, G3SEK
Sent: 04 February 2003 14:54
To: amps@contesting.com
Subject: Re: [Amps] Re: Voodoo "EMF' forces from grid current pulses
2 wrote:
>The grid wires in all of the shorted 3-500Z and 3-400Z tubes that I
>have autopsied appear to be straight. I have never seen a bent grid.
>The bent element is the thoriated-tungsten filament helix.
>
>>you will have to come up with another mechanism, one that can generate
some
>REAL
>>force.
>>
>There is no doubt that real force did the bending because real force is
>required to bend a bent filament straight. It typically takes 11-G for
>c. 40-seconds, with the filament operating at c. 5.6V, to straighten
>the
>filament.
Fine - so where *did* the force come from that bent it? Eric has just
shown that the EM force between two parallel wires is about 1/1000 of an
ounce for the conditions he assumed (two 1in wires separated by 1mm,
each carrying 10A). Even if you dispute the value of the current, you're
still adrift by several orders of magnitude.
>- Eric -- How do you explain:
>1. the grid-filament short often seen in 3-500Zs often follows a
>big-bang?
And just before the event, the grid and filament were already how close?
Nobody knows, because only totally dead tubes are ever autopsied.
>2. the simultaneous burnout of a grid choke made from 28ga Cu wire?
>
That shows that considerable grid current had flowed - but nothing more.
You still don't know whether the blown choke and the grid-filament short
were both caused by the "main event" at the same time; or whether that
event only caused the grid-filament short, which then blew the choke as
a follow-on.
Also there is conflicting evidence. On the one hand, enough grid current
has flowed (somehow) to burn out the choke. On the other hand, it's not
the grid that has bent - it's the filament.
I'm sorry, but the evidence about this whole topic certainly does *not*
"speak for itself"... at least, I can't hear the voices :-)
We're back again to the limitations of autopsy evidence, and the need to
sometimes return an Open Verdict.
--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek
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