That is exactly the point! That is why I said "you might as well use the
tuner in the driver" if you don't have enough capacitance at the cathode
with the L network tuner. Neither is adequate.
You can get a fine match as far as the driver is concerned but it may not be
ok for low IM product generation.
I don't know what the engineers at LDG did or didn't do. All I am saying is
that an L network at the input of a GG amplifier is usually not any better
than using the tuner in your driver. The problem with the L network is that
you can not control the Q with an L network like you can with a Pi network.
The Q is whatever it is as a result of the proper match. You will usually
end up with too little capacitance at the cathode. That is why you don't see
amplifiers built using them.
73
Gary K4FMX
73
Gary K4FMX
> -----Original Message-----
> From: k7rdx [mailto:k7rdx@charter.net]
> Sent: Friday, March 24, 2006 1:47 PM
> To: garyschafer@comcast.net; amps@contesting.com
> Subject: Re: [Amps] Tuned input board on SB-220
>
> 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
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> >
> >
> >
> > _______________________________________________
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