[AMPS] SB-220 Smoke Test

[Tom Rauch]

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, 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.
 

73, Tom W8JI
w8ji@contesting.com

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