> Bottom line, the mods fixed the arcing, and I spent less than $3.00.
> I'd like to ask Tom why these work -- he seems only to say that
> parasitics don't exist, and the mods don't make sense. If that's the
> case, why is my amp now working so much better? The filiment mod is
> very clear to me, same with the step-start mod. Why is this such a big
> deal? If you make your own suppressors, you'll spend very little, and
> certainly won't hurt anything.
You can hurt VHF stability Joe. The Measures suppressors I have measured
actually increase VHF Q.
What Rich overlooks is his suppressors with lower Rp are in SERIES with a
long system. In that case, lower series resistance means higher Q in the
system.
What they do accomplish, and it can be an advantage in some cases, is the
nichrome suppressors reduce Q at the operating frequency! They have the
largest Q reduction change near dc, and actually de-Q the circuit less at
VHF than a conventional suppressor.
If you do an internet search, you will see both Rich and I sent suppressors
to N7WS. Rich did not even have his stock suppressor tested, Wes tested a
DUPLICATE of the 80A/B suppressor made from nichrome. The results of that
test showed the nichrome suppressor that was were identical to the
conventional suppressor had the same VHF characteristics, but less Q at HF.
Keep in mind this was not a stock Measures suppressor, but rather one with
considerably more inductance. The stock suppressor actually has higher VHF Q
when measured in the anode system.
If you read my page on tube arcs and gettering, it is quite easy to
understand that after some number of arcs or operation 3-500Z's that are not
pumped down well enough will degass themselves. Rich also DOES include some
useful mods, so all of his mods are not "bad". Some are. Some aren't.
What I object to is the single-minded claim that virtually all arcs and
virtually all failures are caused by parasitics, and the great harm that has
done to basic knowledge in our hobby.
> Also, if parasitics don't exist or are "Voodoo", why are there
> suppressors on just about every amp or tube transmitter??
I'm not and have never said all amps are stable WITHOUT suppressors. Some
amps are are stable without them, some require them.
What I am saying is if you have a tank circuit arc, you had better look for
one of many possible causes. The most likely one, barring defective
components, is how you tune the amplifer. Historically VHF parasitics are
not a likely cause of switch or tube arcs. There are very solid
easy-to-understand technical reasons for this, that can be explained and
proven by measurements.
The most likely source of tube arcs are defects in the tube, as a matter of
fact it is nearly impossible for a healthy tube in an HF amplifier to arc
from a VHF parasitic and work normally at HF at rated power! The most likely
cause of tank arcs are problems at or near the operating frequency, or at
lower frequencies, where reactances are high enough to allow high voltages
to occur.
You'll find virtually all engineers and experienced technical people agree
on this, and only person leads the "conspiricy" campaign.
I relate this parasitic campain closely to my wife and her "creative
medicines". She is constantly telling me how health foods with no value
"cure" her friends. There is no arguing the point, they take a pill and the
illness eventually disappears. She gave me eye pills because I was having
vision problems, and I threw them in the trash. Two weeks later my eye was
fine.
I suspect just laying the nichrome on the amplifier cover, while replacing
the bad parts in the amp, would do the same thing.
73 Tom
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