[AMPS] Suppressors, measurements, and acrimonious blather

measures 2@vc.net
Thu, 3 Aug 2000 15:11:30 -0700


>
>Paul wrote:
>>
>> > The only useful
>> > goal with today's technology is to not allow the parasitic oscillation 
>>to
>> > start in the first place.
>>
>>Help me here.  Isn't this the purpose of the suppressor?  That is , it's
>>function in design is not only to limit parasitic currents to a "negligible
>>level," but more importantly "suppress" the oscillation from occuring "in
>>the first place?"
>
>Your point is precisely mine.  The function of a parasitic suppressor in 
>today's environment is no longer mere suppression, but outright prevention  
>This was not the case in the 1920's.  Many articles were written concerning 
>the design of filters that would filter out the spurious oscillations that 
>everybody expected to exist.  This is why I am suspicious when a designer 
>uses 1920s theories to design one of today's devices.  The purpose is 
>different today than it was "back then".  

 "back then" VHF parasitic suppressors were never used to absorb the 
considerable energy of the actual oscillation.  Like today, they were 
used to reduce VHF amplification at the anode-resonance.  

>  Unless, of course, one is using a 
>valve from "back then".
>
>> > There is no need to pound repetitively
>> > on the nail of suppressor Q when a few hours work with a nearly free
>> > software package will show whether it makes sense to do so or not.
>>
>>Unless you believe that modeling is not perfect in all cases and measuring
>>resonances in the completed, constructed circuit is a better attempt.  
>>Seems
>>there's an analogy to be made between the accuracy of circuit modeling and
>>the accuracy of antenna modeling software when ground effects are
>>considered.
>
With proper modeling a three element Yagi can have 12db gain.  

>The person who is performing modelling correctly endeavours to model all of 
>the stray elements, in addition to the intended elements.  I have not seen a 
>case yet where a model could not be derived for a real-world application.  
>Proper modelling always is a back-and-forth activity between the model and 
>the manifestation.  In the end, you will have an accurate model, and a 
>physical implementation with extremely predictable behaviour.  

    [chortle].  There is assuredly nothing predictable about parasites.  
Murphy was right.  Things are more complicated than they look.  

>Without the 
>model, you cannot produce such predictability, and without the physical 
>implementation, you cannot test the model.
>
>>I too am perplexed by the ongoing suppressor controversey and it's function
>>seems to be nearly as mystical as that accorded by the dreaded balun.  I
>>question the placement of some type of anode suppressor in nearly every
>>commercially-manufactured amateur amplifiers when most of the same
>>manufacturers would have you believe that 1) their amplifiers are 
>>ultimately
>>stable, and 2) suppressors are not required in "well-engineered" designs.
>>If conditions 1 & 2 are met, isn't it ridiculous to include the suppressors
>>in their designs?  Or, is the inclusion of the suppressor in their
>>amplifiers that little bit of insurance against "the unknown?"
>
>I cannot speak for the behaviour of other manufacturers.  I have used 
>suppressors myself, but only after measurements proved that they were 
>required.  There are some valves which, due to their physical size, are 
>difficult to tame.
>
>In commercial industry, the topic simply does not come up.  If your 
>measurements demonstrate that you need a suppressor, you use one.  Why it 
>occupies so much email bandwidth in this circle is really quite a puzzle to 
>me.
>
It is a puzzle to me as well.  Virtually every thing was known by 1935, 
yet the taurine feculence and hairpull continues.  .  
>
cheers, Fred

-  Rich..., 805.386.3734, www.vcnet.com/measures.  
end


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