>I strongly challenge this assertion. I know of no mechanism within the realm
>of classical EM field theory to account for this. I am assuming you are
>referring to the normal force that would accompany two current-carrying
>conductors which are in parallel proximity to each other.
>
Have you ever been to a welding shop and observed what happens to
arc-welder cables when an arc is struck? I have and I saw the cables
jump about on the floor.
>To illustrate the folly here, try the following numbers, which are based
>upon
>basic physics ( see any good Intro E&M book - Kraus&Carver e.g.) I
>calculated the force (which itself is based upon the Lorenz force which
>exists between a moving electron (a 'current') and a current carrying
>conductor nearby.)
>
> I assumed 2 wires each 1" long and separated by 1mm, which I believe would
>be representative of the grid-cathode geometry in a large transmitting tube.
>With a current of 10 Amperes in each wire (which would no-doubt vaporize any
>grid wire I ever saw)
At its maximum ratings of 4000VDC and 250MHz, the grid in an 8877 quite
happily carries more than 42A-rms. Since there are 108 gold-plated
rectangular bars in the grid to share the current burden, under 0.4A
flows in each grid bar - so there is no heat problem. note -- The AC
grid current results from the grid-anode C of 10pF and a potential of c.
2650V-rms at the anode. However, AC grid-current does not exert a net
force on the grid.
>the attractive force between the two wires is a
>whopping .0005N (multiply X ,22 for pounds). I don't think that is going to
>be bending any wires. And that was assuming the ridiculous value of 10A. for
>the current pulse, which I am assuming is quais-DC.
Yes
>If it is an AC field,
>especially at RF, the force would also oscillate with no net (average)
>force.
>
Agreed
>So if you want us the believe that the voodoo parasitics
"Voodoo parasitics" is a term brandished by W8JI. Do you perhaps know
him?
>cause a current
>flow which generates a strong enough lateral force to damage the wires,
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.
- Eric -- How do you explain:
1. the grid-filament short often seen in 3-500Zs often follows a
big-bang?
2. the simultaneous burnout of a grid choke made from 28ga Cu wire?
- R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K,
www.vcnet.com/measures.
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