[Amps] Amp Supply LK800 trouble

[Thomas Carlsson]

Load cap has no effect!
Does this happen on all bands?
May be the fixed cap's that are inserted in parallell with Load cap...
switched in various quantities depending on band. Checked that thet are
switched properly? And other end of those cap's properly earthed? I had
problems with the earth side.
73, PY2ZXU/SM0CXU/HZ1EX

On Thu, Aug 21, 2008 at 4:49 PM, <kk2ed at comcast.net> wrote:

> Correct - blocking cap in series from the tube anode/parasitic junction
> with the plate choke, over to the PI network's coil.
>
> The unit had a 1000pf since day one, so I don't believe that is the issue.
> The idle current looks fine, so it appears the bias circuit is working.
>
> Strange.....
>
> -------------- Original message --------------
> From: "Bob Maser" <bmaser at tampabay.rr.com>
>
> > The blocking cap should be in series with the tube anode and the coil of
> the
> > Pi network. The RF choke output connects between the tube anode and the
> > blocking cap. Is that the way it is connected? Also, I am surprised that
> > the blocking cap is only 1000pf. 2000pf is what my Henry amp has and all
> my
> > home brew amps have had at least 2000pf, but I don't think that the
> > difference between 1000 and 2000pf would cause what you're seeing. I
> would
> > check to see what the bias is set to. I am not familiar with the LK800
> but
> > I would think that it is using a 12V Zener in the centertap of the
> filament
> > transformer secondary.
> >
> > Good luck,
> > Bob W6TR
> > ----- Original Message -----
> > From:
>  > To:
> > Sent: Thursday, August 21, 2008 1:07 PM
> > Subject: [Amps] Amp Supply LK800 trouble
> >
> >
> > > Good afternoon,
> > > I am still trying to help a friend get his LK800A amp going. Last
> visit,
> > > we thought the 1000pf plate blocking doorknob was bad and not passing
> RF,
> > > as the amp would draw 1A + of plate current, but no RF was appearing at
> > > the output. The plate and tune caps seemed to make no difference when
> > > tuned.
> > > Well, fast forward, and we replaced the 1000pf doorknob cap. Now, we
> are
> > > seeing about 500w make it to the antenna, and the Plate tuning has some
> > > effect, and max power does in fact equal min plate current (dip), give
> or
> > > take a few ma. However, the loading control is having ZERO effect, and
> > > is affecting the output.
> > > Close inspection revealed no signes of bad connections or arcing. We
> > > bypassed the vacuum relay to rule out relay issues, and ohm-ed out the
> > > tank coils and bandswitch.
> > > Studying the schematic and checking the components, everything looks
> good.
> > > The circuit is quite simple - plate bypass cap from the plate choke,
> > > tapped coil, load/tune varicaps, then the relay. I'm missing something
> > > somewhere...
> > > We also pulled the three tubes, tried a spare set, same results. Also
> > > tried one at a time, same thing, so I think the tubes aren't an issue.
> > > Any ideas?
> > > Thanks
> > > Eric KE2D
> > > KE2D
> > > _______________________________________________
> > > Amps mailing list
> > > Amps at contesting.com
> > > http://lists.contesting.com/mailman/listinfo/amps
> >
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>



-- 
Thomas, PY2ZXU/SM0CXU