While we are on the subject can you explain to me how I can calculate the
circulating current in a tank?
thanks,
KRS
----- Original Message -----
From: jeff millar <jeff@wa1hco.mv.com>
To: <amps@contesting.com>; Phil (VA3UX) <phil@vaxxine.com>
Sent: Wednesday, April 04, 2001 10:13 PM
Subject: Re: [AMPS] 4-1000A Project
>
> Here's another way to look a Q that I've never seen discussed
> before. (There's probably a reason for that but maybe is helps
> someone)
>
> You don't have to look at a pi-net as impedance transformation.
> The goal is to create enough current to feed the coax. 1500W
> requires 5.5A rms and a tube doesn't produce nearly that much.
> Since the feed line connects to the tank, then more than 5.5A
> must be circulating in the tank for the coax to pick off. So,
> design the tank to provide enough Q to get more than 5.5A
> circulating.
>
> The impedance of the Pi-net's output load capacitor forms a
> voltage divider with the tank coil. The less load C, the
> higher its impedance and the more of the tank's circulating
> current goes into the feedline. If you replaced the output C with
> a variable L, it would work very similarly...but variable L isn't
> easy to make.
>
> The standard formula, Q = sqrt( Zin / Zout ), defines the
> current multiplication ratio. For example, for Zin=5000 Zin
> and Zout=50, that's ratio=100 or Q=10. Impedance ratio is
> voltage (or current) squared. In other words, the tank
> multiplies the (RMS RF) plate current by 10 and gets it to
> the coax. The circulating current divides between the load
> C and the coax so the Q must go a bit higher.
>
> It's perfectly possible to use a higher Q than the minimum.
> This means more circulating current and more resistive losses.
> The output load C will have a higher value (lower impedance) to
> route a smaller fraction of the circulating current to the coax.
>
> The only other reason to pick a particular Q comes from a
> bit of simulation I did. At just the right Q, changing the loading
> capacitor doesn't require adjustment of the tune C. I remember
> using a Henry 2K on 75M that acted that way. Crank
> the load up and down and the tuning remained perfect.
>
> If anyone's interested I can drag out the work
>
> jeff, wa1hco
>
> ----- Original Message -----
> From: Phil (VA3UX) <phil@vaxxine.com>
> To: <amps@contesting.com>
> Sent: Wednesday, April 04, 2001 9:44 PM
> Subject: Re: [AMPS] 4-1000A Project
>
>
> >
> > At 09:14 PM 4/4/2001 -0400, you wrote:
> > >
> > >
> > >A Q of 12 is NOT some kind of magic number. It is a suggestion,
> > >and efficiency varies only a small amount if the Q is 20 or 6 if it is
> > >done with good tank components.
> > >
> > >12 is a number that makes people feel good, more than making
> > >their amps work good. The best Q might be 6 or it might be 15...it
> > >all depends.
> > >
> >
> > "It all depends ".... on what ? Finish the thought for the benefit of
the
> > poor guy out there that's trying to learn.
> >
> > This discussion has completely overlooked the attenuation of harmonics
as
> a
> > function of tank Q. You guys need to keep in mind that this thread
> started
> > with a request for advice from someone wanting to build their first
4-1000
> > amp. I haven't seen all that much good advice so far; just a bunch of
> > incomplete thoughts and a 4-1000 "expert" that has repeatedly
"bespoken"
> > himself.
> >
> > Phil
> >
> >
> > >As Phil said, play with a roller and watch what happens. If you are
> > >looking for a noticeable efficiency peak...it won't happen.
> > >
> > >What you do with the input circuit can have more to do with
> > >efficiency than tank Q in many cases.
> > >73, Tom W8JI
> > >W8JI@contesting.com
> > >
> > >--
> > >FAQ on WWW: http://www.contesting.com/FAQ/amps
> > >Submissions: amps@contesting.com
> > >Administrative requests: amps-REQUEST@contesting.com
> > >Problems: owner-amps@contesting.com
> > >
> > >
> > >
> >
> >
> > --
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> > Problems: owner-amps@contesting.com
> >
> >
>
>
> --
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