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[AMPS] CENTURION HELP

To: <amps@contesting.com>
Subject: [AMPS] CENTURION HELP
From: measures@vc.net (Rich Measures)
Date: Fri, 5 Sep 97 21:51:25 -0800
>According to a friend who had one, the early 
>CENTURIANS kept full idle current,
>even in the stand-by mode!  
>
The only way this could happen is if the bias potential during receive is 
not what it is supposed to be.  

>Apparently, they also had problems with the
>BIAS  transistor which could explain excessive
>current conditions.  Check the bias voltages
>and components.
>
Agreed, Tom.  There must have been a large current surge through the 
3-500Zs for the 15A-rated bias transistor to short.  If the measured 
potential between the filament CT and the chassis is zero V, I'm guessing 
C-E shorted transistor. 
-  Possible Causes  -
1.  Anode to grid short caused by defective anode-cooler spotwelds (Eimac 
only). -/- Visually inspect anode cooler alignment. 
2.  Air in envelope due to leaking glass/metal seal.  -/-  Test vacuum at 
8kV on a high pot. 
3.  Intermittent VHF oscillation.  -/-  Measure the ohms of the VHF 
suppressor resistor.  Measure grid-filament breakdown potential.  If the 
breakdown V is less than 5 or 6 kV, a bent filament helix is indicated.  
IMO, such oscillations can bend the filament helix.  [See "Parasitics 
Revisited" in the 9/94 *QST*].  Also inspect 10m contacts on bandswitch.  
Damaged contacts indicate that such an oscillation may have occurred.  
 

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


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