[Amps] R. MEASURES PRAYERS ANSWERED

[Pete Smith]

At 08:20 AM 6/2/2006, Gudguyham at aol.com wrote:
> 
>In a message dated 6/1/2006 11:55:24 P.M. Eastern Standard Time,  
>craxd1 at verizon.net 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