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To: "k7fm" <>
From: R L Measures <>
Date: Fri, 2 Jun 2006 04:36:50 -0700
List-post: <>
On Jun 1, 2006, at 8:18 PM, k7fm wrote:

> "I have had dozens of Sb-220 amps in my almost 40 years as a ham.   
> Most  of
> the parasitic suppressors I have changed had their carbon resistors  
> change
> value enough to make them not as effective as suppressors should  
> be.  Most of the
> time a change of resistors will tame a quirky Sb-220."
> Let us follow this statement with basic logic.
> 1.  The SB-220 becomes unstable when the carbon resistor changes  
> value.

The carbon-comp R changes value by an amount not adequately explained  
by simple aging.  For example, a 300% to 500% increase in R in one  
day is not what I would call normal aging.  Also, such resistors show  
no outward indication of extreme age.

> 2.  When that happens, ham A changes out the parasitic suppressor  
> by installing Rich's nichrome suppressor kit, which just happens to  
> include an excellent and stable replacement resistor for the aged  
> carbon resistor.
> 3.  Ham A installs the kit, complete with the new and stable  
> replacement resistor.
> 4.  The SB-220 is stable again.
> 5.  Grateful ham A exclaims to the world that it is Rich's  
> marvelous suppressor fixed the problem.

The first guy to use this type of parasitic oscillation suppressor  
was Mr. F. E. Handy, and it's described on p.72 of the 1926 Amateur  
Radio Handbook.
> It seems the poor resistor has been neglected and is not receiving  
> the credit it deserves.
> I am not trying to discredit Rich's research or opinions.  I just  
> want to give a little more credit to the resistor.  It seems under  
> appreciated in this whole affair.

Matsushita does deserve credit for making incredibly overload- 
resistant MOF resistors, but there's more to the story, Colin.

> Colin  K7FM

R L MEASURES, AG6K. 805-386-3734

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