he SB-220If I were to have ran the test, I would have ran it on
knowingly squirelly amps (ones folks said went into oscillations,
etc) instead of ones that were operating, and never showed a sign of
doing it. It's easy to take 2-3 good acting amps and run a test to
dis-prove parasitic oscillations. Evidently, the one doing the test
never done enough service work in his life, nor actually hands-on
built enough amps to have actually seen this phenomenon. One can set
at a drawing board or computer all day long designing amps, quoting
theory, and never have actually done the work enough to see the
problems. I've seen this time and time again in engineering offices.
A good engineer will take the input from the assembly floor, QC,
service shop, and especially customers to heart, not dismiss it.
On Jun 1, 2006, at 8:53 PM, Will Matney wrote:
> I think what Rich is saying is that when the suppressor is found to
> be bad by either an open or out of tolerance resistor, it may be
> better to change the whole thing using the resistance wire as the
> old original article suggests that he referred too years ago. Just
> changing the resistor certainly can cure the problem,
Changing out the R does not lower Q. The need is to reduce VHF
amplification in order to discourage VHF parasitic oscillation, and
that means lowering VHF-Q. If <15nH, 25w MOF resistors were
available, a suppressor with lower Q could be made with Cu wire by
increasing R-supp and increasing L-supp. However, without such a
resistor, Q can be lowered approx. 2/3 by using #22-AWG Ni-Cr wire
and the most durable 3w rated MOF resistors made.
> but the kit could actually be better than the original design by
> dropping the Q more than it was in the original suppressor design
> using copper wire. I've used suppressors with copper coils for all
> new amps I've ever built because that's what everyone else did.
> I've personally seen squirelly amps that suppressors cured. I have
> also seen two amps of the same model act totally different, one
> being squirelly and one not with no noticeable changes between the
> As a matter of fact, I've seen some run fine without the
> suppressors, but another of the same model need them. In Heathkit
> especially they can change from amp to amp because different folks
> built them and
> I have seen layout changes between each one.
There's apparently some difference in VHF amplification between tubes
from the same production lot.
> The one supposed test I seen on the net which was very flawed, was
> meant solely to discredit the suppressors.
The laugher about his scientific test on the SB-220 proving tha it
can't oscillate, is that during a conversation with him c. December,
1990, he told me that he had repaired approx. 400, SB-220s, and that
he saw parasitic-oscillation damage in most of them. When I pointed
out to him that the VHF suppressor design in the SB-220 was the same
as the design of the suppressor in amplifiers he designed for
Ameritron, he blew a fuse and began speaking so loudly into the
telephone that my wife could hear his voice across the room like we
had a speaker phone, which we did not.
Denial of reality, the greatest human malady.
> *********** REPLY SEPARATOR ***********
> On 6/1/06 at 8:18 PM k7fm wrote:
>> "I have had dozens of Sb-220 amps in my almost 40 years as a ham.
>> the parasitic suppressors I have changed had their carbon
>> resistors change
>> value enough to make them not as effective as suppressors should
>> be. Most
>> of the
>> time a change of resistors will tame a quirky Sb-220."
>> Let us follow this statement with basic logic.
>> 1. The SB-220 becomes unstable when the carbon resistor changes
>> 2. When that happens, ham A changes out the parasitic suppressor by
>> installing Rich's nichrome suppressor kit, which just happens to
>> excellent and stable replacement resistor for the aged carbon
>> 3. Ham A installs the kit, complete with the new and stable
>> 4. The SB-220 is stable again.
>> 5. Grateful ham A exclaims to the world that it is Rich's marvelous
>> suppressor fixed the problem.
>> It seems the poor resistor has been neglected and is not receiving
>> credit it deserves.
>> I am not trying to discredit Rich's research or opinions. I just
>> want to
>> give a little more credit to the resistor. It seems under
>> appreciated in
>> this whole affair.
>> Colin K7FM
>> Amps mailing list
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