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[AMPS] big bang

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Subject: [AMPS] big bang
From: (2)
Date: Fri, 14 Sep 2001 09:14:13 -0700
>SB-200, Harbach power supply board, Harbach soft start module, new Cetron
>572b tubes initially burned in for 24 hours with high voltage and cut-off
>bias and with about 10 hours of use on them.
>Turned on amp and big bang sounding like rifle shot.  No smoke, no smell.

//  sounds familiar.  

>Turned off immediately and checked all values and voltages.  All OK.  No
>visual sign of arcing or burning.
>Turned on again and been working fine all week.

//  If the cause had been a (disappearing) "barnacle" or (vanishing) gas, 
the sound would have been barely audible, like the 'tink' in a 
vacuum-capacitor when it arcs at its breakdown potential.

>Anything I should worry about?  Anything I should fix?
//  I would take the precaution of measuring the resistances of the 
suppressor resistors and the resistances of the grid resistors.  A 
resistance indication of more than plus 25% suggests that there could 
have been an intermittent oscillation.   [note:  measuring the resistance 
of a suppressor resistor requires that one end be unsoldered.]  If you 
find signs of arcing on the 80m Tune-C padder's (100pF) switch contacts, 
a parasitic oscillation is more likely -- provided that you weren't 
rapidly switching the bandswitch while transmitting at full-throttle.  
-  If you want to try decreasing the parallel-equivalent  resistance of 
the suppressors, we can send you a parasitic suppressor retrofit kit to 
try.  Also included is glitch protection for the meters, HV-PS and the 
grids.  If you think its bogus, you don't owe us. Otherwise, it's $12.50 
+$1 for postage.  

cheers, Steve

-  R. L. Measures, 805.386.3734, AG6K,  

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