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Re: [Amps] LK500ZB (2 x 3-500Z), most likely cause of zap/arc?

To: <carlclawson@verizon.net>, <amps@contesting.com>
Subject: Re: [Amps] LK500ZB (2 x 3-500Z), most likely cause of zap/arc?
From: bill price <kingofbackswing@hotmail.com>
Date: Sat, 13 Mar 2010 20:40:24 -0500
List-post: <amps@contesting.com">mailto:amps@contesting.com>
Your tubes are gas ie
 
> From: carlclawson@verizon.net
> To: amps@contesting.com
> Date: Sat, 13 Mar 2010 17:35:13 -0800
> Subject: [Amps] LK500ZB (2 x 3-500Z), most likely cause of zap/arc?
> 
> Anyone have an idea of a favorite failure mode that would cause visible and
> audible arcing in the tube compartment? I'm trying to repair one. Put 10 or
> 20 watts drive to it with the tune controls at nominal settings, you get
> maybe 400 mA plate current. Then as soon as you start rotating the tune
> control...Zap! Followed by blown fuse. And blown grid meter shunt resistor. 
> 
> There's no visible damage, except the varnish is peeling in a few places on
> the plate choke. It doesn't look burnt or anything, but does that indicate a
> choke problem? Or just old age?
> 
> >From what I've read on this reflector before, bad parasitic suppressors
> would be my first guess. But the benefit of your experience will be
> appreciated. I don't have a garage full of spare tubes, chokes, and other
> parts that I can swap in so I'd like to go with the best odds before I start
> buying stuff to try.
> 
> 73 and thanks,
> Carl WS7L
> 
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