At 11:29 AM 3/7/00 -0600, Jon Ogden wrote:
> If
>enough power hits the resistors in a spike to destroy them, it will do just
>that - DESTROY them as Peter Chadwick suggests. But is the typical PA
>supply, particularly a commercially made amateur supply capable of supplying
>that much power?
>
>I doubt it.
>
>Jon
Jon,
I have to comment here. Try this experiment:
1) go down to the hardware store and buy a face shield, the kind sold for
grinding and sawing operations.
2) obtain a 2 watt 10 ohm resistor (carbon or metal film, whatever)
3) connect said resistor with one end on you amp HV and the other end dangling.
4) with all safety gear in place and the HV on, use a suitably insulated
tool to touch the open end of the resistor to ground.
5) describe the observed effect to us
6) repeat the above experiment with a current probe/storage oscilloscope in
series with the open end of the resistor.
7) describe the amplitude and duration of the current pulse observed.
Be advised that I have performed the above experiment (albeit without the
face shield or the oscilloscope) hundreds of times. Not by choice.
The "suitably insulated tool" in these cases was either a 4CX250 or a
4CX1000 that must have been birthed in a "poor science" lab someplace.
These tubes have a tendency, without provocation and without damage to
themselves, to go "big bang" at random intervals. I have had them do this
with and without cutoff bias applied, usually at HV turn-on (but not always).
FWIW, I have *NEVER* seen a glass envelope tube do this, or a triode tube
for that matter.
In case you don't really want to do the experiment, I can say that you
probably don't need the face shield. The effect is approximately what you
might expect from zapping the resistor with a "Klingon Disintegrator Ray"
from a Star Trek episode. I have tried to capture the debris by placing the
resistor in a plastic box, but have never seen anything except a bit of
dark soot!
Now after all that, go back and repeat the experiment with a piece of wire
wrapped around the resistor, Nichrome or otherwise. Please describe the effect.
73,
Larry - W7IUV
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