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[AMPS] G2DAF

To: <amps@contesting.com>
Subject: [AMPS] G2DAF
From: measures@vc.net (Rich Measures)
Date: Thu, 15 Jul 1999 04:46:41 -0700


>
>> ..... //  Another example
>> is Maxwell's conjugate matching theorem.  If it were 100% true, amplifiers
>> could be no more than 50% efficient.  .  
>
>And the logic behind that statement is???
>
?  Power transfer is maximal when the resistance of the load equals the 
internal of the generator.  At this point, efficiency is 50%.   However, 
in practice amplifiers are c.60% efficient.  

>> >For example, Collins had a spotless reputation of good designs, 
>> >yet they somehow came up with a goofy idea that lifting the grids 
>> >of a GG triode class AB2 PA with high reactance capacitors added 
>> >"negative" feedback.
>> 
>> ?  To find out who's goofy, take a dipmeter and measure the 811A grid
>> resonance in a Collins 30L-1 amplifier.  Short the grid to gnd capacitor
>> by soldering a strip of copper foil from the grid terminal to ground.  
>> Remeasure the dip frequency.  If the dip frequency decreases with the
>> short in place, Collins did not goof.
>
>Or you could measure with the correct instrument 

?  Translation:  A dipmeter indicates that the grid-resonance in the 
30L-1 Decreased in freq. when the small grid-gnd cap. was shorted by the 
copper strap.  

>and measure 
>something meaningful like feedthrough power, and see feedthrough 
>power increases when the capacitors are installed.
>
?  Natcherly, this is a complex, replete with self-delusive pitfalls, 
procedure that requires special test equipment which few of us are likely 
to have.  . . .  Tom's continuing battle with the dipmeter invites 
comparison to the Thirty Years War.  .  

>It's a bad idea, for a multiband amplifier, to increase unwanted 
>feedthrough. 

?  The hat trick is to move the  grid's parallel-resonance (where 
feedback/feedthrough is maximal) away from the anode-resonace, where 
damped wave VHF ringing takes place whenever the anode current changes. 

>Especially when the tubes have too much feedback to 
>be stable without neutralization when the grids are grounded.
>
?  In the world of VHF, a grid can not be absolutely, positively brought 
to ground potential.  
>
-  later, Tom


Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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