>
>> Question: How relevant is the percentage delta when the Q is ~ 2.0? In
>> other words, is this percentage change at ~ 2.0 as important as a say a
>> 46% change in Q from 50 to 73?
>>
>> -Paul, W9AC
>
>If we can maintain a "low-noise" conversation, you can decide for
>yourself.
>
>First, we should understand this. The suppressor Wes measured
>was NOT the suppressor Rich sells.
Rich does not sell parasitic suppressors. He sells parts to construct
them and information. Customers build the suppressors. The
resistance-wire suppressor that was tested by Wes was built by Wes.
>The suppressor Wes measured was a duplicate of the stock Ameritron
suppressor with
>nichrome wire.
>
>Wes did that to eliminate all variables and only consider the
>change in wire. The stock suppressor Rich sells actually produces
>high VHF Q in the anode system of the AL80A series of PA. It
>does NOT reduce VHF Q. It reduces ten meter Q, and 15 meter Q,
>but not VHF Q.
>
The excursion on the wide river in the Land of Pharoahs continues.
>There is a good technical reason for that, and it's easy to see. But
>first more to your point...
>
>Q of the suppressor, by itself, is not a direct factor in parasitic
>suppression. The suppressor is part of a distributed system of
>wires and components that have a complex impedance (resistance
>and reactance). The suppressor adds another impedance in series
>with this system (not a "Q" value), and the complex impedance
>(resistance and reactance) of the suppressor modifies the anode
>system impedance.
>
>What you want to do is add enough resistance to stabilize the PA
>(if it needs it) at the frequency where the tube oscillates. In order to
>make s significant change the impedance of the suppressor has to
>be large compared to the impedance of the path it is in.
>
>Consider the simple case where the suppressor a pure resistance.
>If the anode circuit presents a series impedance of 10 -20j ohms,
>the addition of 100 ohms of additional ESR (equiv series
>resistance) will greatly change anode system impedance and Q. Q
>of the anode system will drop from 2 to about 0.2.
>
>If the added resistance was 1 ohm, there would hardly be an anode
>Q change!
>
>In both cases, Q of the "suppressor" was zero.
>
>You have to know what the impedance of the anode system is, and
>what you want to do, before you can decide if one suppressor is
>better than another.
>
Tom -- would you say that higher VHF Q is better in the anode's resonant
circuit than lower VHF Q?
>There is a procedure for doing that. Most hams don't do that, but if
>thousands of units are manufactured it is a good idea to look at
>little things like this.
>
>If you remove the stock suppressor in an AL80A or B, and replace
>it with a hairpin of nichrome, the VHF anode Q of the suppressor
>where the amplifier has a tendency to oscillate increase
>dramatically. That isn't normally a problem, because the amplifier
>barely oscillates up there anyway even when the suppressor is
>totally removed. Rich's suppressor doesn't really do any harm to
>stability, even though it increases VHF Q slightly. The only ill effect
>is it reduces tank Q, mostly on ten meters.
>
Tank Q is defined as the ratio of Xc (of theTune-C) and (HF) RL.
>His suppressors are a partial solution in amps like the Clipperton,
>because they can be made to repeatedly oscillate near ten meters.
>In that case, the low ten meter Q helps stabilize the PA.
>
>De-Q'ing the HF tank also helps reduce arcing in the tank, because
>it reduces peak voltages. That can help if you mistune the PA, or
>have a load fault.
The suppressor is not in the path of circulating current in the tank.
>
>So the Q of the suppressor, by itself, is a meaningless parameter.
>The actual important parameter is the impedance of the suppressor
>and how it affects the impedance of the tank.
>
>That's why if you have an unstable amplifier with long thin anode
>leads, the suppressor must have more turns with a higher
>resistance in the suppressor. The shorter the anode leads and the
>wider, and the lower the tuning capacitor impedance at VHF, the
>lower the inductance and resistance in the suppressor can be for
>the same anode system dampening.
>
>You want the parallel equivalent impedance of the suppressor to be
>large compared to the anode system impedance at the point where
>the suppressor is added.
>
The tapdance.
Why did you stonewall the question on who designed Dennis Had's original
AL-80?
>
end
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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