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From: Pete Smith <>
Date: Fri, 02 Jun 2006 08:41:09 -0400
List-post: <>
At 08:20 AM 6/2/2006, wrote:
>In a message dated 6/1/2006 11:55:24 P.M. Eastern Standard Time,  
> writes:
>The one  supposed test I seen on the net which was very flawed, was meant 
>solely to  discredit the suppressors. If I were to have ran the test, I would 
>have ran it  on knowingly squirelly amps
>Can someone tell me why some SB-220's have stability problems and why  others 
>don't?  Can we identify the difference between them?   OR......Are all 
>SB-220's not satable?

My SB-220, which was evidently built by a very skilled OT, is unconditionally 
stable.  Construction quality, proper lead lengths, etc. are one consideration. 
 Another may be the tubes used - I have heard that certain manufacturers' 
3-500s have higher gain than others.  My tubes are all Eimacs, still going 
strong after 30 years.  Finally, there were some changes made during the SB-220 
production run that may have affected stability; one I have heard of is that 
the spacing of the tuning capacitor was increased to prevent arcing, which had 
the effect of shifting the weakest link to the bandswitch.  Whether any of 
these changes may have affected stability is beyond me...

I did not mean to imply in my earlier message that SB-220s don't need parasitic 
suppressors, or that needing suppressors is somehow a bad thing.  This whole 
suppressor argument has achieved theological status, with about as much hope of 
being resolved as one of those debates.  Cooler heads have observed that 
sensible amplifier designers determine empirically whether an amplifier is 
stable or not, and apply suppressors if indicated.

73, Pete N4ZR 

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