[AMPS] Suppressors, measurements, and acrimonious blather
Thu, 3 Aug 2000 15:11:30 -0700
>> > The only useful
>> > goal with today's technology is to not allow the parasitic oscillation
>> > 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.
>>there's an analogy to be made between the accuracy of circuit modeling and
>>the accuracy of antenna modeling software when ground effects are
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.
>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
>>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
It is a puzzle to me as well. Virtually every thing was known by 1935,
yet the taurine feculence and hairpull continues. .
- Rich..., 805.386.3734, www.vcnet.com/measures.
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