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[AMPS] Stability Question

To: <>
Subject: [AMPS] Stability Question
From: (Rich Measures)
Date: Tue, 9 Feb 1999 04:42:44 -0800

>>>Here's how I am testing:
>>>Key up amp, no RF, Ctune at min, Cload at max, open circuit on output 
>>> (ie: no antenna or dummy load - no coax attached).  I figured this 
>>>would be worst case.
>>Sure is and not a reliable test of the amps operational stability. 

?  The setting of L and C-load are not substantive factors, nor is the HF 
load, because L is pretty much like a vhf choke.  .  The resonant circuit 
that supports a vhf parasite is formed by lead inductance between the 
tube and C-tune, and by the anode-C of the tube.  

>>Try it with real world tuning values and then remove the load.  

?  Transient currents are one way to encourage a vhf parasite.  This 
means driving the amplifier with a load connected.  I would not remove 
the load.   

>> A good layout should then be stable.
>>In a perfect world what you are trying should work but the 4-1000A at
>>that voltage is just asking to take off, why encourage it?  There are
>>even some commercial ham amps that would not pass that test.
>OK.  Well, I guess I am just of the school that wants an amplifier to be 
>bullet proof.  Under "reasonable"  real world values, I have no 
>oscillation.  It's just when my turns counter on my UCS-300 gets very low 
>(about 5 with a minimum of 0) that I have the problem.  It's probably 
>barely a crank from its absolute minimum.  Realistically, I'd never take 
>it that low even on 10m.

?  sounds like standing on thin ice.  


R. L. Measures, 805-386-3734, AG6K,  

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