[Elecraft] Negative resistance overcome

[Tom, W6WW]

Bob,

Your advice paid off.  I spent a few hours trying to troubleshoot the
"negative resistance" and finally gave up as you suggested.  It had to be
stray 60 cycle power getting rectified somewhere, but I could never pin it
down.

I thought proceeding to the next step would show the problem up in a
different way, but everything went fine.  First QSO was last night and the
report was FB.

Now, all I need is an antenna more than 3 feet high.

73,
Tom, W6WW
K2 #3453


----- Original Message -----
From: "R. Coakley" <rcoakley@maine.rr.com>
To: "Tom, W6WW" <tom@cwx.com>
Sent: Thursday, July 17, 2003 9:35 PM
Subject: Re: [Elecraft] KPA100 resistance check shows negative resistance


> Tom,
>
> I had a problem with my KPA100 involving J3 measurements.  Mine turned out
> to be a stupid mistake - wrong part at U7 - BUT I made a boatload of
> measurements at J3 while troubleshooting.  I got the small negative
voltage,
> strange ohmmeter readings: starting huge, dropping then rising on one DVM,
> negative resistance and changing (like your measurements) on another, and
a
> typical RC charging increase on an Analog meter.  After rechecking all
diode
> and electrolytic directions, I decided to go ahead with the next steps.
> That turned out to be the thing to do.  All was OK, and after I replaced
U7
> with the correct op amp, I had a working PA.  So, I would suggest going
> ahead.
>
> 73  Bob   KX1E
> ----- Original Message -----
> From: "Tom, W6WW" <tom@cwx.com>
> To: "- Elecraft" <elecraft@mailman.qth.net>
> Sent: Thursday, July 17, 2003 10:31 AM
> Subject: [Elecraft] KPA100 resistance check shows negative resistance
>
>
> > I need help with my KPA100 construction.
> >
> > Performing the resistance checks on page 41 just after assembling the
> KPA100
> > board to the heat sink, I find a NEGATIVE resistance ( -2 meg) on my DMM
> at
> > the J3 + lead.  Further checking shows a persistent voltage of -0.35
volts
> > at that J3 + lead with no power connected to the board.
> >
> > With an analog meter, the resistance check varies greatly depending on
the
> > scale used, but the negative voltage persists.
> >
> > I have tried shorting the leads to ground in an attempt to dissapate any
> > charge on the electrolytic  capacitor, but the results stay the same.
> >
> > Any ideas about how to proceed would be greatly appreciated.
> >
> > 73,
> > Tom, W6WW
> > K2 #3453
> >
> >
> > 73,
> > Tom, W6WW
> > K2 #3453
> >
> >
> >
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>
>
>


73,
Tom, W6WW
K2 #3453