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[Amps] Alpha 374A problems

To: <>
Subject: [Amps] Alpha 374A problems
From: (2)
Date: Fri, 23 Aug 2002 18:50:44 -0700
>Hi Folks
>I am working on my sons amp which blew up with a loud bang. What
>I have found so far is one tube with a grid to cathode short
>when filament voltage is applied. 

**  grid/cathode shorts are typically caused by cathode flaking.  [ 
photos in Sept/Oct 1990 *QST* ]  This can result from inadequate warm-up, 
more than 350mA continuous cathode-current, or an intermittent parasitic 
oscillation.  I would test the tubes with a high-pot tester for the 
presence of gas or evaporated gold.  Leakage should be under 5uA @ 5kV 
positive and negative on the anode with the grid grounded.  More leakage 
current with positive V on the anode means loose gold.  

-  R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,  

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