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Re: 70cm amps

Here's my experience:

TE Systems 4452G and Mirage B2530G.  Both about 6 years old.
The TE worked great out of the box and has worked great ever since.  The
Mirage suffered problems.  It was sensitive to the length of the jumper
between the exciter and the amp, and the length specified by Mirage did not
work.  It was back at the factory twice in the first six months.  After that
it has been fine.  In both cases they are fed with short lengths of #4
primary wire.  The PS is a 70 amp Astron.  I have also powered them with
large "deep cycle" batteries.  Don't skimp on DC cable size or power supply
on these large 12 V. amps.  Both are mounted in an open rack with plenty of
ventilation.  I have considered aux. cooling fans, but neither seems to get
too hot.  I believe there are different heat sink designs available (the G
suffix).  Be sure to specify the "best" heat sink.

73 - JC,k0hps@amsat.org

----- Original Message -----
From: Miles Mann <Miles.Mann@ind.alcatel.com>
To: Walls, Jim R <WALLSJR@sce.com>
Cc: "'Gary \"Joe\" Mayfield'" <ka0yos@AMSAT.Org>; <w7lrd@juno.com>;
'AMSAT-BB list' <amsat-bb@AMSAT.Org>
Sent: Thursday, April 27, 2000 12:38 PM
Subject: Re: [amsat-bb] 70cm amps

> Hi all
> Everyone may have an amplifier horror story. Some amps are better than
> others.  I have tried three major brands in the 100 plus watt capacity.
> Here are a few usage stories.
> RF concepts:
>   (model?)  10in 170 out meters
> Ran good, plenty of power.
> Power meets or exceeds specifications.
> Built in SWR overload circuit works most of the time.
> Can only tolerate limited abuse.
> Fried the finals the first time when I feed the wrong antenna for too
> long.
> Fried the finals the second time when a friend borrowed the amp and
> drove
> the 10 watt input with 100 watts.
> Overall I was please with the amp (3 years usage) and sold it working to
> a friend who
> is still using it.  I replced it becaues my radio puts out 25-30 watts.
> And it
> is very importatn to make sure you do not over drive your Amp.
> TE Systems:
> Model? 25-30in, 300-400 output, 2-meters.
> No swr protections on the High power models, so you must
> be careful.
> Blew finals transmitting into the coax with out an antenna.
> TE fixed it quickly, I paid for the finals, labor was free.
> The heat sink is a little small for the power load,
> so i run a small fan to keep it cool.
> I have been using this one extensively for ssb and Mir satellite
> operations for over 3 years.
> TE Systems:
> Model? 25in, 150 output, 435mc.
> This model is very voltage sensitive.
> At 14.0 volts i get the full published 170 watts.
> However at my normal 13.8 volts the output is aprox 150 watts.
> The other models are not as sensitive to input voltage.
> The heat sink on the 70cm 170 amp is the same size
> as the 2meter 400 watt amp.  So I assume the 2meter
> heat sink is too small.  This amp seems to handle normal
> QSO without too much heat.
> In operation for 3 years, no problems.
> I use it for SSTV VSB, SSB and FM satellite.
> Mirage:
> model? 25 in, 300 out, 2-meters
> After carefully checking all antenna connections and
> using the pre-amp to verify the cable connections.
> This amp blew on the first key down.
> The problem was caused by a last minute assembly change
> to a resistor.  A 10-watt resistor was not in stock, so someone
> tied two 5 watt resistors together standing up.  The pig-tail leads
> touched the metal case and caused the failure.
> Two weeks later a replacement arrived.
> this one too, failed on the first key down.
> I do not know what caused the second failure, i just
> switched to TE systems.
> All amps will eventually blow.  Most failures are caused by
> bad coax or antenna related problems, or user error.
> good luck and becareful.
> Miles
> "Walls, Jim R" wrote:
>  >
>  > Bob - W7LRD asked:
>  >
>  > > My recent attempts at AO-10 clearly show I need an amp.  Before I
>  > > out the check, I would like to know what the collective wisdom is on
>  > > subject.  A short note- e-mail direct please.
>  >
>  > ----------
>  > Then Gary "Joe" Mayfield said:
>  >
>  > >     I had very good luck with a T.E. Systems amp.  And I know they
>  > > are still available.  Burghardt's here in town has them.
>  >
>  > > http://www.burghardt-amateur.com
>  >
>  > Just my opinion based on our experiences with TE Systems amps - AVOID
>  > LIKE THE PLAGUE!  Our club has the better part of a dozen of them in
use on
>  > our repeater network (13 repeaters on 220).  To date we have had 100%
>  > failures on them.  We could not get TE systems to fix them even on
>  > warrantee.  In fact several years ago we had sent two amps in for
>  > repair and after 11 months, they had not even opened the shipping box!
>  > finally drove over to their facility and picked up the box (still
>  > un-opened).  We had a RF design engineer take a look at them and he
>  > that the electrical design was right out of a Motorola Application note
>  > (except that they pushed the transistors pretty hard), but the thermal
>  > design was horrible.  We have redesigned the thermal design and they
>  > better, but we will NEVER buy another one.
>  > Professionally, my employer has a bunch of their amps in a commercial
>  > and have also had a very high failure rate.
>  >
>  > 73
>  > -------------------------
>  > Jim Walls - K6CCC
>  > k6ccc@amsat.org
>  > http://home.earthlink.net/~k6ccc
>  > Mobile Radio Operations
>  > Southern California Edison Co.
>  > Ofc:  626-302-8515    FAX:  626-302-9999
>  > Res:  626-914-4641
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