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Re: [Amps] IM distortion and such

To: "Tom W8JI" <>
Subject: Re: [Amps] IM distortion and such
From: R L Measures <>
Date: Wed, 28 Jun 2006 07:42:33 -0700
List-post: <>
On Jun 28, 2006, at 3:23 AM, Tom W8JI wrote:

>>> Tom said:
>>>> Even a curved line does not necessarily produce
>>> IM3 or IM5. (harmful IM3 is 2 * F1 - F2,  or 2*F2-F1, IM5
>>> is
>>> 3*F1-2*F2, 3*F2-2*F1 and so on through all odd-order
>>> products).<
>  On Jun 27, 2006, at 10:12 PM, Peter Chadwick wrote:
>>> If it's a square law curve, for example, there are NO
>>> third order  products (at least from that stage). Then
>>> again, some curvature can  lead to cancellation and an
>>> improvement in IMD at some power level.
> Rich AG6K wrote:
>> RE: constant current curves:  I do not believe that a
>> constantly  changing slope (i. e., a curved line) has this
>> magical ability. .
> Unfortunately Rich even if **you** don't believe what nearly
> every good electrical engineer in the world knows to be a
> fact, including all the people at Eimac who design tubes, it
> does not change anything about how things work. The good
> news for all of us is we can all learn something new, unless
> we decide not to.

The slope of the line represents the transfer characteristic.  In the  
region where where the line is straight, the transfer characteristic  
is constant and amplification is linear therein.
> Peter wrote:
>>> The data sheet absolute maxima are the ones that really
>>> count -  exceed those, and you can have problems getting
>>> warranties honoured.
> Rich wrote:
>> How would the manufacturer determine how much peak current
>> had ever  been emitted from a directly-heated cathode?
> They can't, because that parameter does not harm tube life
> in any way in a thoriated tungsten tube. Excessive cathode
> current by itself can only be harmful in a metal-oxide
> cathode indirectly heated tube.

> This thread consumed days, and the results are:
> 1.) Emission current in directly heated tubes is not a
> parameter that affects tube life.


> 2.) Transfer function of the overall system affects splatter
> in this application, not a single particular constant
> current curve. Thus the tube information is being used
> incorrectly by some.

It's about slope.  If the slope is steep, amplification is low.  If  
the slope is shallow amplification is high.  In order to achieve  
linearity, amplification must remain constant during the conduction  

> 3.) A slope in transfer function does not necessarily mean
> splatter, and can actually reduce splatter.

Transfer function is slope, Tom.

> 4.) Your basis for claiming major splatter problems comes
> from noticing two stations over the air that seemed wide,
> rather than actual tests or measurements.

not two.

> 5.) Facts don't matter, the only thing that matters is what
> we accept.

sounds kinda like hubris
> 73, Tom
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R L MEASURES, AG6K. 805-386-3734

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