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Re: [Amps] Surge resistor

To: "'Vic K2VCO'" <>,"'Rick Stealey'" <>
Subject: Re: [Amps] Surge resistor
From: "Gary Schafer" <>
Date: Wed, 21 Mar 2007 12:11:13 -0400
List-post: <>

> -----Original Message-----
> From: [] On
> Behalf Of Vic K2VCO
> Sent: Wednesday, March 21, 2007 11:28 AM
> To: Rick Stealey
> Cc:
> Subject: Re: [Amps] Surge resistor
> Rick Stealey wrote:
> > Tom, W8JI, says:
> >> The small glitch resistors in your amp don't do a darned thing
> >
> > I am in the process of finishing up my 8877 amp, and the plans I am
> > using show a 0.6 ohm 1 watter and a 50 ohm 50 watter in series.  So in
> > the event of a flashover (milliseconds ?) the 0.5 ohmer is supposed to
> > blow open?  I can't see the value of the 50 watter.  In case of
> > extremely high plate current, such as hitting it with full drive and no
> > load, say 2 amps of plate current flows and even then the big resistor
> > only drops 100 volts, and heats up 200 watts. I wouldn't expect a
> > wirewound power resistor to fail immediately under these circumstances,
> > and I can't see how it is protecting anything.
> > What am I missing here?  Is the 50 watter the wrong type?
> The 50 ohm surge resistor is designed to reduce the very high current
> that would occur if there were an arc in the tube as a result of gas, or
> a 'whisker' on a metallic structure in the tube, for example.  This
> current could be hundreds of amps (the power is stored in the filter
> capacitors). A good surge resistor will allow a small arc to occur,
> which may clear the gas or whisker, and then the amp will continue to
> work normally. Without the resistor, the huge current may destroy the
> tube, RF choke, etc.
> --
> 73,
> Vic, K2VCO
> Fresno CA

Dare we say that a glitch can also be caused by a parasitic oscillation.

Gary  K4FMX

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