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Re: [TenTec] repairs

To: tentec@contesting.com
Subject: Re: [TenTec] repairs
From: Douglas <sparks06524@yahoo.com>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Thu, 13 Jul 2006 09:22:29 -0700 (PDT)
List-post: <mailto:tentec@contesting.com>

> Message: 1
> Date: Thu, 13 Jul 2006 11:57:25 -0400
> From: "ROBERT CARROLL" <w2wg@comcast.net>
> Subject: Re: [TenTec] repairs
> To: "'Discussion of Ten-Tec Equipment'"
> <tentec@contesting.com>
> Message-ID:
> <07f601c6a695$09190390$6401a8c0@D79s9d51>
> Content-Type: text/plain;     charset="US-ASCII"
> I had recently questioned whether the Omni or
> similar rigs had a design
> problem if they needed to be protected by an Airpax
> breaker.  One of the
> Airpax advocates responded that the issue was not
> oscillation but the
> ability of the rigs to put out full power into a
> mismatch causing a quick
> thermal failure due to inadequate heat-sinking.  To
> me that sounded like a
> questionable explanation, but again a misdesign
> problem if true.  But these
> failures do indeed sound like oscillation problems. 
> Strange indeed.  My
> condolences.  It is a painful experience to have to
> ship a rig out for
> repair.
> 73
> Bob W2WG

Asuuming that there is no component failure such as
bad ALC diodes, as another poster mentioned, I've
never heard of multiple failures of the finals in
Ten-Tec rigs.

I've run Ten-Tec Tritons, Omni C/D's, Corsairs and
Paragons without ever having such a problem. As far as
I know, the Omni VI's finals are no different from
those in the Paragon

The heatsinking is perfectly adequate for continuous
key down operation for long periods of time.

The reason why the Airpax breakers are recommended
while using NON-Ten_Tec supplies is that Ten-Tec's
design philosphy was to not have a large amount of
power fold-back if the operating SWR was high. ALC
protects the finals in Ten-Tec rigs but only to a
limtied extent.

Let's say that the SWR was 3 to one on the low side.
The operating impedance would be roughly +_J16 ohms.
Under those low impedance conditions, high collector
current flow can occur in the output transistors.
If such high current was sustained, damage to the
final transistors could result. Ten-Ten owners manuals
explain this.

I've heard of the finals oscillating if the power
supply was dropping out of regulation. Have you
checked the supply voltage under full power key down
conditions? RF feedback may be getting into your

Another reason for oscillations is an antenna that is
presenting a complex impedance, generally not near 1:1
SWR, to your rig.  If you are able to load full power
output into a dummy load with no problems, I'd suspect
bad grounding or something wrong with your antenna

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