[AMRadio] Pi-Net vs Link Couple


bcarling at cfl.rr.com bcarling at cfl.rr.com
Tue Sep 27 08:09:27 EDT 2005


Are you talking about plate AND screen modulation?
Or just screen mod?

On 23 Sep 2005 at 1:06, Bob Bruhns wrote:

> This is the screen-choke self modulation
> technique.  Screen current is affected by the
> modulated plate voltage, and the screen choke lets
> the screen vary above and below the screen suply
> voltage according to screen current.  If the choke
> is large enough (you need 10 to 20 henries), the
> screen can follow the modulating audio waveform on
> the plate, and the net result is a happy,
> self-modulated screen grid.
> 
> To really tweak this, some people have added a
> small compensating capacitor from modulated B+ to
> the screen, to act as a capacitive voltage divider
> with the screen bypass cap, and maintain screen
> modulation percentage at high frequencies.
> 
> The choke will only allow audio variations, so the
> screen will be held at the DC voltage of the
> screen supply.  When used along with some fixed
> control grid bias, this eliminates the need for a
> screen clamp-tube.
> 
>   Bacon, WA3WDR
> 
> 
> ----- Original Message ----- 
> From: "W5OMR/Geoff" <w5omr at satx.rr.com>
> To: "Discussion of AM Radio"
> <amradio at mailman.qth.net>
> Sent: Thursday, September 22, 2005 10:28 PM
> Subject: Re: [AMRadio] Pi-Net vs Link Couple
> 
> 
> > Darrell, WA5VGO wrote:
> >
> > > Triodes are great for grounded grid, but for
> class C, why fight
> > > neutralization? Use a power grid tube. Sure
> you need a screen supply,
> > > but consider the paybacks. No neutralization;
> at least on the lower
> > > frequencies, and low drive requirements. I
> realize modulating it is a
> > > little trickier, but I've never had the Eimac
> system of placing a
> > > reactor in the screen supply to fail to do the
> trick.
> > >
> > > Darrell, WA5VGO
> >
> >
> > that's interesting, Darrell... a reactor in the
> screen supply.  Are you
> > capacitivly coupling it, as well?  No, that
> can't be - the screens need
> > to be DC voltage.  However, the choke effectivly
> kills any stray
> > capacitances...
> >
> > hmmmmm
> >
> > Great discussion, so far.  Looking forward to
> more.
> >
> > Hope you guys are hunkered down for the
> hurricane.  Kingwood, TX may be
> > on the west side of the storm, but it's gonna be
> a big'un.
> >
> > --
> > 73 = Best Regards,
> > -Geoff/W5OMR
> >
> >
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