Amps
[Top] [All Lists]

[AMPS] Filament breakage

To: <amps@contesting.com>
Subject: [AMPS] Filament breakage
From: w8jitom@postoffice.worldnet.att.net (w8jitom@postoffice.worldnet.att.net)
Date: Sun, 11 May 1997 14:35:39 +0000
It would be nice if one of the proponents of "parasitics breaking 
filaments" could mathematically demonstrate how current levels 
intense enough to produce magnetic forces strong enough to break the 
filament could possibly occur from the alleged oscillation.

It's a pretty straight forward calculation. The only parameters 
needed to find the mechanical force are distance, current intensity, 
and current distribution.

We can assume the current distribution would be equally spread 
over the total area of the heated electron emitting surface. With a 
single wire in a "V" shape, at half the distance from the upper end 
of the filament we could have a maximum of half the potential 
saturated emission current flowing past that point.

With a 811A or 572B, we could make a generous allowance using the 
following data:

The filament power is about 25 watts. The best thoriated tungsten 
materials produce less than 125 mA per watt of peak saturated 
emission current. This potentially allows 3 amperes total emission 
current flowing in the filament (if the grid was driven to hundreds 
or thousands of volts positive), divided between four vertical wires.

(The filament looks like an "M".)

Emission current at the bottom of the middle wires center point 
(this is the electrical center of the filament) would be zero, and 
current at the two outer ends of the filament (at the point where the 
filament connection exits the tube) would each be 1.5 amperes. 
The total emission current flowing into the tube would be 3 
amperes. 

The primary physical force driving the wires would be between two 
adjacent wires. This would be the additional force produced by the 
field interaction of 1.25 amperes in one wire moving in a direction 
opposite .375 amperes in the other wire.

This allegedly LARGE force (from one conductor carrying 1.25 amperes 
while another carries .375 amperes)  supposedly SNAPS the filament 
like a twig, while the 4 amperes of normal filament current (evenly 
distributed in the series wires, so each opposing wire has four 
amperes creating a magnetic field) has no effect at all.

We are supposed to believe the wires are so close to breaking that an 
additional few percent of magnetic induced force (a pull of a few 
grams)  breaks the wires, even though that small amount of additional 
current would only occur if the oscillation was so severe it drove 
the tube into complete saturation!!!

Anyone want to run 4 amperes through a linear wire and try to pick up 
a steel pin 1/4 inch away?

I do have a personal opinion about this. Such obvious non-sense 
theories are a waste of time and energy. They demonstrate how 
quickly some people leap to conclusions without thinking about the 
problem at hand, and give answers that can't be supported by physics.
73, Tom W8JI 

--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com

<Prev in Thread] Current Thread [Next in Thread>