[ETO_Alpha] 87A problem

Sun, 19 Jan 2003 22:29:25 -0700

Hi All,

So far the only problems I have seen with PIN diodes in an 87a all had one
of the following reasons: The operator was running in excess of 2300W out
into an >1.8:1VSWR for an extended period of time (nah we don't do that
right?).The constant use of high power(>2200W) somehow eats away on the
power diodes they get leaky over time. Throw in a little VSWR and you are in
for it.
Also continuous usage into a VSWR just below the trip point could do it.
Usage of the amp with trap antennas and arcing (also arcing of antennas that
have high Q coils with >2000 w out could do it).  The voltage will ring down
the cable and it can reach a value that can turn on the receive diodes....
BUM. The last scenario is dependent on the electrical distance to the ark
and where the arc is happening on the trap (high Q coil ect). Not all arcing
antennas will damage the amp.

No other failure mode is known here and I repair ALPHA amps (all models)
since 1990.

And yes there is a way to install a vacuum relay ( and a fast input relay)
it is not easy as you will have to fake out some of the protection circuit.
Especially the read-back circuits.Only if you are intimately familiar with
the circuit should you try to do this. And of course you will void all
warranty.
You  could change the read-back values in the software but this means you
need someone that is willing to tell you the software commands, the eeprom
location of the value to be changed, and the access code.

John K7NEP

----- Original Message -----
From: "jbattin" <[email protected]>
To: "Ragnar Otterstad" <[email protected]>; <[email protected]>
Sent: Sunday, January 19, 2003 10:02 PM
Subject: Re: [ETO_Alpha] 87A problem

> That is strange ... I have three 87a's and no problem with diodes.
> John K9DX
> ----- Original Message -----
> From: "Ragnar Otterstad" <[email protected]>
> To: <[email protected]>
> Sent: Wednesday, January 01, 2003 9:14 PM
> Subject: [ETO_Alpha] 87A problem
>
>
> > MY 87A has a reliability problem, i.e. the PIN diodes break down too
> > frequently.
> >
> > Has somebody done a vacuum-relay modification to solvethe PIN diode
> problem
> > once and for all ?
> >
> > 73   HNY
> >
> > Rag Otterstad    LA5HE also JW5HE OZ8RO
> > located in Telemark - home of skiing.
> >
> > My antenna "farm" can be found on HTTP://no.photos.yahoo.com/la5he when
> you
> > click on  Radio.
> >
> >
> > Take a look at: http://WWW.visitTelemark.com
> >
> > or  http://www.visitnorway.com
> >
> >
> >
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