----- Original Message -----
From: Larry Molitor <w7iuv@nis4u.com>
To: Jon Ogden <jono@enteract.com>; <Wt8r@aol.com>; <amps@contesting.com>
Sent: Wednesday, March 08, 2000 12:09 AM
Subject: Re: [AMPS] Power Handling of Resistors
>
> 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
>
Now that was funny!!
Cheers Larry!
Conrad G0RUZ
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