[AMPS] Technical Question #1

[Rich Measures]

>> Date:          Thu, 21 May 1998 11:43:40 -0500
>> From:          Jon Ogden <jono@webspun.com>
>
>Hi Jon,
> 
>> I believe there is some neutralization that can be done in GG amps.  The 
>> most important aspect I recall has to do with making sure that there is a 
>> balance between the two tubes.  A single tube amp need not worry about 
>> it, but in 2 tube amps there can be a problem.  Someone please correct me 
>> if I am incorrect.  I don't have Mr. Orr's book handy at the moment.
>
>Don't rely entirely on Mr. Orr's book. That is a collection of data 
>from many sources, and it was never really peer reviewed.
>
Orr was basically a merchandizer, not an originator.  

>Many other books do describe neutralization of GG amps, it is no 
>major feat. Electronic Designers Handbook contains such circuitry, 

Page numbers? 

>as well as many other engineering textbooks. 
>
How about some titles and page numbers? 

>The Heathkit Warrior and Gonset (4) 811A amps were both neutralized, 
>and are much more stable at HF than amps that are not neutralized.
>
The Heathkit Warrior was apparently so unstable that Heath dropped the 
so-called "neutralization" circuit.  This is why the SB-200, SB-220, 
HL-2200, and SB-230 had no neutralization circuit.  
.  .  It is my opinion that G-G amplifiers do not need neutralization at 
the fundamental operating frequency.  A feedback circuit which may 
achieve negative feedback at HF could well provide positive feedback at 
VHF.  .   

>In most parallel tube applications it is not necessary to neutralize 
>the tubes separately.  You simpler invert the phase 180 degrees in a 
>broadband transformer, and couple the filament to the anode.

Does one invert phase at the fundamental frequency, or does one invert 
phase at the anode's VHF resonance?   
>
>The AL-811H and AL-1200 both use this technique. Both are 
>completely stable with any terminations on input and output and at 
>any control setting, unlike amps using the same tubes without 
>neutralization.

Seems like a "friendly" test to me.  .  In the real world, tubes are 
driven, which produces rapid variations in anode-current, which produces 
damped wave ringing at the anode's VHF resonance.  



Rich...

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


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