Re: [amsat-bb] 70cm amps

["Howard Long" <howard@xxxxxxxxxxxxxx>]

Miles,

Am I glad it's not just me who's got an expensive linear story.

I've fried a couple of Mirage D-1010 100W 70cm linears:

o    First it went short across the power supply when using VOX of its own
volition

o    I accidentally unplugged a dummy load whilst testing the power handling
of a phasing harness (the phone rang whilst I was testing, and of course
when I came off the phone I forgot I was still transmitting). The fault blew
so much up that it wasn't really worth repairing.

I'm running only TE-Systems successfully right now, (model 1452G 25in/375out
on 2m, and model 4452G 25in/200out on 70cm). The 2m unit does get quite
warm, though. Another issue for me was that for some reason both units were
supplied with UHF rather than N-type connectors.

I've also run successfully Microset units (model SR-200, 10in/200out on 2m,
and model RU-432-95 10in/100out on 70cm).

None of the above has VSWR protection, although the Mirage and TE-Systems
allegedly have temperature protection.

I think that unless the amp has _reliable_ VSWR protection, care of the
units is essential!

Of course, if I didn't have all that lossy coax from the shack to the
antenna, I'd probably not need a linear at all.

Regards, Howard


----- 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 8:38 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
make
 >  > > out the check, I would like to know what the collective wisdom is on
this
 >  > > 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
THEM
 >  > 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
warrantee
 >  > repair and after 11 months, they had not even opened the shipping box!
We
 >  > 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
said
 >  > 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
are
 >  > better, but we will NEVER buy another one.
 >  > Professionally, my employer has a bunch of their amps in a commercial
system
 >  > 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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