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Re: [Amps] repair of older Command Tech VHF-2000 amp

To: amps@contesting.com
Subject: Re: [Amps] repair of older Command Tech VHF-2000 amp
From: Jim W7RY <w7ry@centurytel.net>
Reply-to: w7ry@centurytel.net
Date: Mon, 14 Oct 2013 15:50:11 -0700
List-post: <amps@contesting.com">mailto:amps@contesting.com>
What kind of coax?

73
Jim W7RY

On 10/14/2013 9:17 AM, Louis Parascondola wrote:
I performed what seemed to be a rather odd repair on an older Command Tech 
VHF-2000.  I thought I would share this since it could possibly affect the HF 
models.  This particular amp like most has a piece of coax that comes off the 
output of the tank circuit and goes over to the antenna relay. In this case a 
harmonic filter.  The coax was affixed to the side of the wall and dove down to 
the bottom and over to the relay. Filter in this case.   There was what seemed 
to be a soft arc to the coax as it bent over the edge and down.  The amp 
exhibited no output whatsoever and acted like there was not antenna connected.  
I tracked down the problem to that coax being internally shorted.  An autopsy 
of the piece of coax was amazing.  Apparently the owner of this amp operated 
digital modes like JT65 so I would think there were many  periods of heavy duty 
cycles.  Apparently over time the dielectric center conductor heated up and 
little by little the wire migrated to the outer edge and
 e
  ventually broke through at the "arc" strain point and shorted to the braid.  
Several inches of the center wire was way far away from the center of the dielectric.  Go 
figure.
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