To: <amps@contesting.com>
>> 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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