> and see. You really have to make several mistakes in layout
> to require neutralization in a GG amp.
> Paul
>
Not true in the least Paul.
A layout has to be extremely poor to require neutralization, but
many tubes have so much anode/cathode feedthrough they require
neutralization no matter what the layout.
A GG pair of 572B's, perfectly shielded and laid out, are actually
not unconditionally stable above 15-25 MHz because of the tube's
internal feedthrough. Four 572's are a real major problem.
While you can sometimes get away with three 811's in parallel GG,
four 811A's are always a problem at higher frequencies. The Collins
30L1 is one of the few unneutralized 811 amps, and has stability
problems above 15 MHz.
3CX1200A7 and D7's have feedthrough problems above 25MHz,
and require neutralization if you expect the anode dip to be
anywhere near maximum grid current, although the Z7 cures that
with a modified grid.
.
73, Tom W8JI
W8JI@contesting.com
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