But if you employ the tuner in the driver, the length of coax to the tube
cathode becomes another issue. I am confident the engineers at LDG as well
as those who tested their tuner boards in amps prior to them releasing the
product for sale,have looked at all the angles,,,All I want to report to
this group is the fact the tuner does a great job for me and if it makes you
happy to question it`s operation then so be it...Jim..K7RDX..
----- Original Message -----
From: "Gary Schafer" <garyschafer@comcast.net>
To: <amps@contesting.com>
Sent: Friday, March 24, 2006 8:47 AM
Subject: Re: [Amps] Tuned input board on SB-220
> With an L network if the tube impedance is lower than the driver impedance
> then there will be a coil to ground at the cathode rather than the needed
> capacitor.
>
> If the cathode impedance is higher than the driver impedance by a small
> (even 3:1) amount then there will be a capacitor on the cathode side of
the
> L network but it will be too small and the Q will be too low for proper
> flywheel effect.
>
> With a tube that has 150 ohms input impedance using an L network to match
to
> 50 ohms will have a capacitance of around 428 pf on 80 meters providing a
Q
> of only around 1.3.
>
> Bill Orr recommends 13 pf/ meter for input capacitance. That would require
> 1040 pf at the tubes cathode for proper harmonic current transfer to
ground.
>
> Proper Q and proper shunt capacitance at the cathode can not usually be
> obtained with an L network. It requires a Pi network to control those
> factors. A parallel tuned tank would also work ok.
>
> With an L network at the tube you can get an impedance match to keep the
> driver happy but you might just as well employ the tuner in the driver to
do
> the same.
>
> 73
> Gary K4FMX
>
> > -----Original Message-----
> > From: Bob Maser [mailto:bmaser@tampabay.rr.com]
> > Sent: Wednesday, March 22, 2006 11:56 PM
> > To: garyschafer@comcast.net
> > Subject: Re: [Amps] Tuned input board on SB-220
> >
> > Not true
> > ----- Original Message -----
> > From: "Gary Schafer" <garyschafer@comcast.net>
> > To: "'noddie'" <noddie@comcast.net>; "'Ed Dial'" <diale@mindspring.com>;
> > <amps@contesting.com>
> > Sent: Wednesday, March 22, 2006 11:22 PM
> > Subject: Re: [Amps] Tuned input board on SB-220
> >
> >
> > > There was some discussion on this board awhile back and wasn't it
> > decided
> > > that the tuner is actually an L network and not a PI? That would make
it
> > > unsuitable as a tuned input network.
> > >
> > > 73
> > > Gary K4FMX
> > >
> > >
> > >> -----Original Message-----
> > >> From: amps-bounces@contesting.com
[mailto:amps-bounces@contesting.com]
> > On
> > >> Behalf Of noddie
> > >> Sent: Wednesday, March 22, 2006 10:10 PM
> > >> To: 'Ed Dial'; amps@contesting.com
> > >> Subject: Re: [Amps] Tuned input board on SB-220
> > >>
> > >>
> > >> The AT-100AMP is what I am going to use on my SB-221, I wish it had
> > been
> > >> around when I build a tuned input board for my Clippertron L, all the
> > >> other
> > >> tuned input boards do not work on the WARC bands and cost 150 dollars
> > >> compared to 125 dollars for the AT-100AMP and this board is automatic
> > >> with
> > >> memories. The only thing you will have to watch out for is that your
> > RF
> > >> choke does not resonate on the WARC bands. I changed my choke to the
> > RF
> > >> Parts one at a cost of 25 bucks, it works for 3-500's and 572b's and
> > will
> > >> not resonate on the WARC bands.
> > >>
> > >> Mike
> > >>
> > >>
> > >> Gentlemen,
> > >>
> > >> I need opinions from the experts that live here. I have an SB-220
> > >> that does an excellent job on the pre-WARC bands, however it doesn't
> > >> like 12 and 17 meters very well, thanks to the tuned input circuit
> > >> from what I understand. I noticed that the good folks at LDG
> > >> Electronics is now selling a stripped version of their AT-100
> > >> autotuner as the AT-100AMP, marketed as an RF amplifier tuned input
> > >> board for homebrews and the like. My question is, could this board be
> > >> fitted into the SB-220 without much pain? Would this solve the WARC
> > >> problem?
> > >>
> > >> If so, would it work in the SB-200 as well? I have no clue with 572s.
> > >>
> > >> Lazy and looking for the simple way out -
> > >>
> > >> Ed
> > >> WA4RYW
> > >>
> > >>
> > >> _______________________________________________
> > >> Amps mailing list
> > >> Amps@contesting.com
> > >> http://lists.contesting.com/mailman/listinfo/amps
> > >>
> > >> _______________________________________________
> > >> Amps mailing list
> > >> Amps@contesting.com
> > >> http://lists.contesting.com/mailman/listinfo/amps
> > >
> > >
> > > _______________________________________________
> > > Amps mailing list
> > > Amps@contesting.com
> > > http://lists.contesting.com/mailman/listinfo/amps
>
>
>
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