Hi Ian,
It's easy to spot someone who has measured or really understands the
cause of a problem.
> With small amounts of grid current, some IMD products will go up but
> others may come down.
<snip>
> One thing is certain, though: anything that puts a major kink in the
> transfer characteristic will increase higher-order IMD. The higher the
> output resistance of the grid supply, the stronger that kink will be
> where the instantaneous grid voltage crosses zero.
> A "read-only" member of this mailing-list has reported an improvement in
> the IMD of a pair of 4-250s on going from class AB1 to class AB2. This
> may be surprising, but knowing his identity I trust his data. It is no
> coincidence that he uses a shunt-stabilized grid bias supply with a low
> output impedance.
Anyone who has ever watched IMD products on a spectrum
analyzer would appreciate your words Ian. As bias, drive and loading
are changed some IMD products get worse as others get better. But
make no mistake about it, pulling the grid way up negative during
peaks or letting the screen supply waddle around makes the amp
trashy.
73, Tom W8JI
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