Well, at the start of the CQWW CW Contest, my SB-220
smoked. One of a near new set of Eimac 3-500Z's developed
a grid-cathode short and smoked the grid bypass choke.
After some research, it appears that this is a common
failure mode of a VHF parasitic. I will be changing
the parasitic suppressors out but I am also considering
strapping the grids directly to the chassis. I assume
that a mod is also needed in the grid current metering
circuitry.
My questions:
Have you done a directly grounded grid mod to your SB-220?
Did it do the job of stabilizing the amp?
Any additional mods required (grid metering, etc.) ?
Thanks and 73 de Mike, W1NR
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**************** Give Every Man His Dew **************
Michael A. McCarthy, President
Everest Engineering Corporation, Consultants
4 Barnes Circle, Marlborough, MA 01752
(508) 460-6737, FAX (508) 460-7951
mailto:w1nr@eecorp.com
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