[AMPS] Re:

[Rich Measures]

>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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