On Jun 2, 2006, at 5:41 AM, Pete Smith wrote:
> At 08:20 AM 6/2/2006, Gudguyham@aol.com wrote:
>> In a message dated 6/1/2006 11:55:24 P.M. Eastern Standard Time,
>> email@example.com 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
>> 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.
Amen, and so far there is no explanation that makes sense.
> 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...
Increased Tune-C spacing did not improve stability, but sales of
bandswitches improved considerably
> 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.
Unfortunately, the test for fundamental instability does not test for
W7MOI purchased a new Henry 2K-4A. Nothing at all happened when he
rotated the tune and load controls with zero drive. After almost 8-
years of almost daily use, he announced that the 2k-4A was perfectly
stable. Within a week, he heard a big bang and subsequently
discovered that both 3-500Zs had grid-fil shorts.
> 73, Pete N4ZR
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