>Dick,
>
>GREAT posting. Really good!
>
>>
>> 2) Never met Ian, but the gut feeling grows that anyone who challenges him
>>in the area of network analysis or any fundamental EE stuff has a real good
>>chance of losing. Very respectable stuff, Ian - I appreciate it.
However, adding a bit of X to make one's calculations come out more
favourably, undoubtedly gives one a leg up.
>
>He's very brilliant. And has the patience to teach some of us
>knuckleheads (like me) a thing or two!
>>
>>3) Too many guys are talking about output circuit "Q" without specifying
>>"loaded Q" or "UNloaded Q."
Most amplifier builders use Eimac's definition.
>>They're very different things and the ambiguity
>>can cause confusion. I absolutely agree with Tom, Pete and others that
>>inadequate loading of a class AB, B or C amplifier, whether the output
>>network is "old-fashioned" parallel resonant, a pi, or a pi-L, results in
>>excessive "LOADED Q" of the tank circuit which can AND DOES often create
>>peak rf voltages several times the DC plate voltage. And it's not magic or
>>very hard to understand.
In a Heath SB-220 the peak anode potential under a worst case condition
measured about 128% of the supply voltage. .
>>I defer to Ian, however, for the rigorous proof,
>>because it's easy to see that he won't have to work as hard as I would to
>>dig it out(!)
>
>Agreed.
It seems to me that adding a bit of X wherever needed does not a proof
make.
>>
>>4) Maybe I've missed someone else's similar description, but I believe the
>>logical, conventional, and easiest-to-understand explanation of how a
>>common parasitic suppressor works is that [a], it does not ABSORB VHF/UHF
>>parasitic power or energy, but PREVENTS (or "suppresses") the parasitic
>>oscillation from occurring in the first place; [b] it does so by lowering
>>the loaded "Q" of the existing parasitic resonance(s?) in the anode circuit
>>to the point where feedback loop gain at the parasitic resonant frequency
>>(-ies) is too low to support oscillation.
Agreed -- i.e., the hat trick is to reduce the voltage amplification at
the anode's VHF-resonance to one or less - by reducing VHF-Q. Reducing Q
is the job of a VHF suppressor. . . It seems that the question at hand
is this: Is it easier to make a low-Q suppressor with resistance-wire or
with copper-wire? . According to Wes' measurements, for similar
suppressors, at 100MHz, the copper-wire suppressor had a Q of 2.2, and
the resistance-wire suppressor had a Q of 1.5. 2.2/1.5=1.46. . Is 46%
more VHF-Q mo' betta?
However, the copper-wire suppressor had 34% more L and 9% more R, so my
guess is that test was weighted roughly 18% in favor of the copper-wire
suppressor.
>>The trick, if you want to call it
>>that, is to introduce enough loss (resistance) into the parasitic resonant
>>circuit to do the job without absorbing so much of the
>>fundamental-frequency power as to either overheat itself or unduly reduce
>>amp efficiency/output.
>
>Again, agreed. This was one of my original conclusions after reading
>everybodys stuff.
>>
Verily. And what happens to the Q of a VHF suppressor when R opens up?
According to Wes' measurements, at 100MHz, Q increased roughly 30x. .
Welcome to Oscillatorville, folks.
>.......
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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