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[Amps] 3-500Z parasitic wows

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Subject: [Amps] 3-500Z parasitic wows
From: (Phil Clements)
Date: Thu, 22 Aug 2002 18:27:04 -0500
> At 03:57 PM 8/22/02 -0400, WA2BPE wrote:
> >...Had this happen to me with an old SB220 destroying one tube; luckily (??),
> >they were about to be replaced anyways.  Later investigation showed that the
> >resistors in the parasitic chokes had increased between 5 & 10x their
> >value.  I was "fortunate" - only the tube arced with no other damage.
> Which "this" is that?  A parasitic, or a random grid/filament short, or
> arcing due to a mismatched load, or a Rocky Point arc?  There are lots of
> things that can happen with a manually tuned amp, and I'd be more inclined
> to look at other things to blame besides a workhorse tube that is probably
> in more amateur amps than any other...
As we all know, most of the amps made before the 90's have little or
no protection devices installed, leaving the door wide open for
everything from a critter looking for a warm home to an "oscillation
condition," not to mention human error in the heat of battle. The
archives of this reflector are full of preventative cures for ills that
have emerged over the years as amps become antiquated. A
sure bet is that eventually a tube is going to come to the end of
its life. The name of the game is to protect all the other components
 in the box when it decides to go out in a violent manner.

Phil, K5PC

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