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Re: [Amps] IM distortion and such

To: <>
Subject: Re: [Amps] IM distortion and such
From: "Tom W8JI" <>
Date: Wed, 28 Jun 2006 06:23:36 -0400
List-post: <>
>> 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.

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.
3.) A slope in transfer function does not necessarily mean 
splatter, and can actually reduce splatter.
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.
5.) Facts don't matter, the only thing that matters is what 
we accept.

73, Tom 

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