All,
The "jumping cables" can also be seen if you've ever jump started a
car. Watch what happens when the car with the "dead" battery is
cranked. This is of course a substantial amount of instantanious
current. Not knowing all the fancy laws, I can only go on empirical
data. Jumper cables are huge compared to a tungsten filiment. The
current to make a filiment move must be significantly less. I've never
autopsied a tube and probably never will, but I **DO** know this: My
TL-922 burned a bandswitch and arced on tune-up constantly (especially
on 75m). Once I installed the mods recommended by Rich, this baby
hasn't arced, spit, sputtered, or any other term you might be able to
think of. The physics of a filiment-to-grid short may be "VooDoo" to
me, but simple VHF oscillations and the stabilization/suppression mods
aren't. And they worked.
Joe,
N3JI
--- 2 <2@vc.net> wrote:
>
>
> >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.
> end
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
__________________________________________________
Do you Yahoo!?
Yahoo! Mail Plus - Powerful. Affordable. Sign up now.
http://mailplus.yahoo.com
|