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@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@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
>
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