>
>Hi Tim,
>
>I normally do that mod to SB-220's and other amps.
>
>> So what benefit did directly grounding the grids bring?
>
>If you put a lug by each grid pin, you can actually remove turns
>from the suppressor without running into instability compared to a
>similar test with the grids grounded through the caps.
>
>I don't remove turns from the suppressors in operating PA's since
>the 220 suppressor is fine as is,
? When I spoke with Tom on the telephone, he told me that he had
repaired about 400 SB-220s and that he had seen lots of parasitic damage.
>but only use this as an A-B test
>indicator of how stability changed.
>
>> More output on any or all bands for the same drive power?
>
>Well, if you mod the PA for 160 M it works a lot better there. If not,
>you only see a slight gain flatness improvement. Also, you see
>less input SWR change as the tuning control is adjusted. That's a
>good sign also.
>
> > The same output on any or all bands for LESS drive power?
>
>Not a great amount, but there is a slight improvement in gain.
>
>> A better VSWR between the radio and the amplifier input? The stock 220
>> input VSWR on 10 and 15 is pretty poor.
>
>I've always has to redo the input, so I can't say which way it goes
>without the changes. I do know the input SWR varies less as the
>plate control is rotated around the plate current "dip" and maximum
>output is closer to dip center.
>
>> Does the amp tune smother on 10 and 15?
>
>As above.
>
In a stock SB-220, there is typically a slight double-dip on 40m. After
lowering the Rp of suppressors, there isn't.
>
end
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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