There is no reason that all amps, GG or otherwise, can't be or shouldn't
be neutralizied. At the same time one must understand that while some
tube and circuit designs are known to function quite well without
neutraliziation, others (those where there is a high grid to anode C
value) do require it.
However, don't confuse the need for neutralization with the need for
parasitic suppression. They aren't the same by a long shot.
Unfortunately, both show up as an instability......flash, bang!
To see if neutralization is required, a study of IMD products must be
undertaken.
A truly stable amp must be able to operate without any evidence of
instability regardless of the input load or output load and with any
combination of tuning adjustments. Stable is stable.
73
Bob K4TAX
carl seyersdahl wrote:
>
> I've known about neutralizing amps for many years, and repaired many of
> them for the gov't but I don't recall ever seeing a GG amp neutralized.
> Since the plate and cathode ckts. are in phase with each other, and 180
> degrees out of phase with the grid, it follows that , directly from plate to
> ground one would need a phase inversion. this of course could be done with a
> coil and a cap, but it doesn't seem to me that the feedback would remain
> exactly what it needs to be on all bands in a bandswitching amp. in the old
> days, with grid driven amps, and single band, it seemed to work well, but
> today it's a different story. all this is what I learned over the years, and
> of course I could be slightly off base or have forgotten my basics(it's been
> a looong time) and I was out of the game for nearly 30 years!!!I've recently
> repaired some sb200's and one sb220 and the owners are happy with them(and
> the amps aren't neutralized), so maybe I haven't totally lost touch with
> reality.Any comments?? (I can still learn!!) carl / kz5ca
>
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