W8JI has some great info in his web site about this.
http://www.w8ji.com/loading_amplifier.htm
73
Jim W7RY
On Wed, May 19, 2010 at 10:49 AM, Bill Dzurilla <billdz.geo@yahoo.com>wrote:
> Carl and all,
>
> I may have lucked out this time. I was able to obtain full 1200 watts
> output on both 80 and 160 meters simply by refusing to turn the Load
> capacitor to less than 4.5. I left the Load cap on 5 and tuned the Plate
> cap for maximum output while slowly increasing drive. The video camera was
> rolling, but no arcing, and no sign of excessive redness in the tubes.
>
> Still not sure everything is 100%. It seems as though the amp wants to see
> less loading, because output went up when I turned the Load cap from 5 to
> 4.5. You can see this in yesterday's video. At the moment of the arc, I
> was turning the Plate cap to the left and output was increasing. The arc
> occurred with Plate at 4 or perhaps even 3.5, so today I just would not go
> below 4.5.
>
> So am I good to go or what? Several folks said right from the start that
> my problem was under-coupling, and it seems they were correct.
>
> 73 and many thanks for all the responses and emails,
> Bill NZ5N
>
> --- On Wed, 5/19/10, Carl <km1h@jeremy.mv.com> wrote:
>
> > From: Carl <km1h@jeremy.mv.com>
> > Subject: Re: [Amps] Drake L-7 arcing on 80m - with video
> > To: "Bill Dzurilla" <billdz.geo@yahoo.com>, amps@contesting.com
> > Date: Wednesday, May 19, 2010, 10:07 AM
> > These old eyes didnt capture all the
> > detail in the video I guess!
> > Unfortunately staked plates cant be removed to smooth and
> > polish.
> > Alternatives would be to retrofit a different cap unless a
> > Drake can be
> > found. Or smooth the bad plates as well as possible and
> > give them a spray
> > coat of acrylic clear from Plasticote or similar.
> >
> > Carl
> > KM1H
> >
> > -----------------
> >
> >
> > Many thanks to all who watched the video and emailed me
> > with ideas. I have
> > watched it 50 times and I'm now convinced that the arc
> > occurred in the plate
> > cap stator that has the white graffiti-like traces, as
> > described in a prior
> > post. The flashes on the coil are just
> > reflections. If you look carefully
> > through the plastic bubble on back of the plate current
> > meter, you can see
> > the arc originating in the plate tuning capacitor.
> >
> > Suggested fixes have included:
> > * replacing the mica caps mounted underneath the rear wafer
> > of the
> > bandswitch,
> > * replacing the plate blocking capacitors,
> > * polishing or totally removing the stator with the white
> > traces,
> > * Carl's suggestion below to try a piece of insulation
> > between the coil and
> > the cap.
> >
> > Have not yet tried any of these suggestions, but please
> > keep the ideas
> > coming.
> >
> > 73, Bill NZ5N
> >
> > --- On Tue, 5/18/10, Carl <km1h@jeremy.mv.com>
> > wrote:
> >
> > > From: Carl <km1h@jeremy.mv.com>
> > > Subject: Re: [Amps] Drake L-7 arcing on 80m
> > > To: "Bill Dzurilla" <billdz.geo@yahoo.com>,
> > amps@contesting.com
> > > Date: Tuesday, May 18, 2010, 10:47 PM
> > > That is strange. Try placing a thin
> > > insulator on top of the cap: teflon, polystyrene,
> > > fiberglass, etc and see if its just the coil or the
> > cap
> > > arcing independently and not from one to the other.
> > >
> > > Also check all RF connections for crystallized solder
> > due
> > > to RF heating. If so suck or wick it off and reflow
> > new
> > > solder.
> > >
> > > Carl
> > > KM1H
> > >
> > >
> > >
> > >
> > >
> > > ----- Original Message ----- From: "Bill Dzurilla"
> > <billdz.geo@yahoo.com>
> > > To: <amps@contesting.com>
> > > Sent: Tuesday, May 18, 2010 10:26 PM
> > > Subject: Re: [Amps] Drake L-7 arcing on 80m
> > >
> > >
> > > Thanks to all who responded on and off line. As
> > > suggested by Carl, I removed the cover and tried it
> > > again. Rig was connected to a Heathkit Cantenna dummy
> > > load. As suggested by several, I set the Load control
> > > to 5 at the start, to prevent under-coupling. I made
> > a
> > > video of the procedure and, as you can see at:
> > > http://www.youtube.com/watch?v=iJRyNQnkEWA
> > > there was arcing again. The arc occurs near the end
> > > of the video clip, at the 1:18 mark. You can see it
> > on
> > > the first 2 turns of the coil that is on top of the
> > Plate
> > > capacitor. Not sure if this is a reflection or if the
> > > coil itself was arcing. I did not see any arcing from
> > > the capacitor.
> > >
> > > Not sure how visible it is on YouTube, but I have
> > watched
> > > this several times in slow motion. You can see a bit
> > > of the rotor of the Load capacitor on the left side of
> > the
> > > screen, and also a bit of the output meter. At least
> > in
> > > slo-mo, you can see output going up as I start to turn
> > the
> > > Load cap to the left, then the tubes start to redden
> > and the
> > > arc occurs.
> > >
> > > If the turning of the Load cap to the left resulted
> > in
> > > under-coupling and caused the arc, I'm not sure how
> > to
> > > proceed, because output was very low with the Load cap
> > set
> > > at 5.
> > >
> > > Comments, ideas, advice?
> > >
> > > 73, Bill NZ5N
> > >
> > > > Take the cover off, bypass the interlock, and do
> > a
> > > visual when in >operation.
> > > > There could be a switch problem or fixed cap
> > causing
> > > the variable to arc.
> > >
> > > > Carl
> > > > KM1H
> > >
> > > > Subject: [Amps] Drake L-7 arcing on 80m
> > > > To: amps@contesting.com
> > > > Message-ID: <28539.87346.qm@web51103.mail.re2.yahoo.com>
> > > > Content-Type: text/plain; charset=us-ascii
> > > >
> > > > Hello,
> > > >
> > > > I recently acquired an L-7 amp and I tried it
> > out
> > > > yesterday. I used my Pro II as the exciter, an
> > amp
> > > > keyer, and a dummy load.
> > > >
> > > > There seems to be some problem on 80,
> > unfortunately.
> > > > On all bands, I started with 20 watts drive and
> > > slowly
> > > > increased the drive while tuning for max output.
> > > > When
> > > > I got up to about 600 watts out on 80, I heard
> > and
> > > saw
> > > > through the meter a blue arc. This happened twice
> > on
> > > > 80, and I did not want to try it again. No arcing
> > at
> > > > all on 40, 20, 15, or 10.
> > > >
> > > > I opened up the amp and everything looks OK,
> > except
> > > for one
> > > > of the 25 or so stators on the plate tuning
> > capacitor
> > > has
> > > > graffiti-like white traces on it. I suspect this
> > is
> > > > the source of the 80m arcing, as the rotor does
> > not go
> > > over
> > > > the spot with the traces when set to 40m and up.
> > I
> > > > have not tried the amp on 160m, but if my theory
> > is
> > > correct
> > > > it would arc on 160 as well as 80.
> > > >
> > > > The capacitor plates are not dented or deformed
> > in
> > > any
> > > > way. Have not tried the amp on the WARC bands.
> > > >
> > > > So, do you think the stator is the source of the
> > > > problem? If yes, is there any fix?
> > > >
> > > > 73, Bill NZ5N
> > >
> > >
> > >
> > >
> > > _______________________________________________
> > > Amps mailing list
> > > Amps@contesting.com
> > > http://lists.contesting.com/mailman/listinfo/amps
> > >
> >
> >
> >
> >
>
>
>
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