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

[Carl]

Where is this visible arcing taking place?

Carl
KM1H


----- Original Message ----- 
From: "Carl Clawson" <carlclawson at verizon.net>
To: <amps at contesting.com>
Sent: Saturday, March 13, 2010 8:35 PM
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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