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Re: [TenTec] Loud fan PS 963

To: tentec@contesting.com
Subject: Re: [TenTec] Loud fan PS 963
From: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Reply-to: geraldj@weather.net, Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Tue, 29 Sep 2009 09:03:25 -0600
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
On Tue, 2009-09-29 at 04:33 +0000, Richards wrote:
> I also did not like the intermittent fan noise, which only comes on 
> occasionally, but is noisy when it does. 
> I purchased an Astron RS-25M for the rig, and use the TT 963 supply for all 
> my accessories, and the fan no longer comes on.  The radio seems happier with 
> the beefier, linear supply.   The accessories are quite happy with more than 
> enough juice available, and the fan never runs.  
Consider the fact that many Tentec radios depend on the current limiting
of the Tentec supply to be the SWR protection for the PA transistors.
That you sacrifice when using the Astron supply which can lead to
sacrificing the PA transistors if the SWR causes excessive PA transistor
current. Unless you insert sensitive fuses or circuit breaker in the DC
line to the radio. For my Corsair II, I use 16 amp fuses that will carry
the normal 20 amps for hours, but will blow faster than the PA
transistors (as I have proven while tuning an antenna tuner at full
power with a brick on the key). The factory chose a magnetic circuit
breaker with minimum delay for that purpose. The fuses I use have a
similar time curve to the breaker.

The my experiences with Astron supplies is that their technology tends
to be old, not taking account the heating of the heat sink, nor using
adequate emitter resistors in the pass transistor group to force good
current sharing, so the pass transistors fail one at a time until the
supply can only run the pilot lights, nothing else because the only
working transistor is the 3 amp driver transistor. That's been
compounded by a lack of thermal heat sink grease at the transistors in
some cases.

> Just MY take.
> ================  Richards -K8JHR  =======================
73, Jerry, K0CQ

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