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

[Mark Bitterlich]

Louis,

This phenonamom used to be seen quite regularly in certain military aircraft 
where coax types such as RG-214, RG-213, RG-217 were used.  Any kind of 
medium to sharp bend at all, co-located with a heat source caused it as you 
mentioned.  Typically around turbine compartments or bleed air lines.

All of these coax runs  were eventually replaced with Teflon dielectric 
types, such as RG-142 & RG-393.    That lesson learned, all of my amps have 
been re-plumbed with the same teflon type coax. :-)

Mark Bitterich
wa3jpy


----- Original Message ----- 
From: "Louis Parascondola" <gudguyham at aol.com>
To: <amps at contesting.com>
Sent: Monday, October 14, 2013 12:17 PM
Subject: [Amps] repair of older Command Tech VHF-2000 amp


>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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