> >How soon we forget things like that.
>
> How soon you forgot our telephone conversation wherein you told me that
> you had seen parasitic-oscillation damage in many of the 400 Heath
> SB-220s you had repaired. I wonder if Tom remember what he said when I
> told him he used essentially the same suppressor design in the SB-1000 ?
No many how many times you repeat that story, it does not become real Rich.
The only stability problem I am or ever have been aware of in a SB220 is the
same one that occurs in other amps using that silly super-cathode circuitry.
I have spice models of a typical grid impedance on my website. It has
nothing to do with VHF, except as it needlessly makes the grid connection
physically longer than needed. This is similar to what VK6APK did. He made
the grids leads long, tying them in common.
That is a bad idea in ANY amplifier, since it moves the frequency of
self-neutralization lower while decreasing the ground effectiveness greatly
at the grids.
73 Tom
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