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[AMPS] Blown TL922A... What to do?

To: <amps@contesting.com>
Subject: [AMPS] Blown TL922A... What to do?
From: 2@vc.net (measures)
Date: Mon, 11 Sep 2000 10:58:26 -0700
>
>> 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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