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[AMPS] FAILURE OF PARASITIC RESISTORS IN AL-811X AMPLIFIER

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Subject: [AMPS] FAILURE OF PARASITIC RESISTORS IN AL-811X AMPLIFIER
From: W8JI@contesting.com (Tom Rauch)
Date: Thu, 2 Mar 2000 20:01:39 -0500
> > Or you can put a series capacitor in series with the R and cancel
> > the reactance at the frequency of instability.
> 
> What is the frequency of instability?

Don't know, I don't have the amplifier in front of me...or even know 
what one it is.

> Therefore what is the reactance?

Don't know.  Same reason as given above.

> On what grounds is it assumed that there is only one frequency of
> instability?

Might not be just one. Some amps have two, like the Clipperton.

> If the "suppressor" is meant to suppress something, why make it even
> more transparent to the something?

The suppressor adds a resistance to the circuit, that somewhat 
equals the system impedance at the frequency of instability. 
Sometimes you need more resistance, sometimes less, 
sometimes a touch of reactance one way or another helps.

It's extremely simple to learn what you need to do, and just do it. 
But it does require knowing what PA is being discussed, and how 
that PA behaves.

However, that is all out of the scope of my reply...which simply and 
correctly said reactance in the resistor is not a problem because it 
can be cancelled. If you know that reactance, and it is very easy to 
learn its value, and you know the problematic frequency...and there 
is generally just one at VHF....you can do a very simple correction 
that has multiple benefits, like significantly less heating of the 
resistor.



> 
> Ciao,
> Ian ZS6BTE
> 
> 
> --
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> 


73, Tom W8JI
w8ji@contesting.com

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