[AMRadio] Pi-Net vs Link Couple


Mike Dorworth,K4XM k4xm at arczip.com
Thu Sep 22 10:48:30 EDT 2005


Ronnie, Hello! The 1 kilowatt Triode Pi-Network Amplifier using the 450TH is
in the Editors and Engineers Handbook 14th Edition. The first of the
handbooks edited by Bill Orr W6SAI. It has the RED cover. It starts on Page
585 in chapter 26-12 and ends on page 589. My scanner got knocked off the
table by the dog and is broken. Been looking for replacement at CHEAP price.
Perhaps some of the other fellows have this handy, if not, in a coupla weeks
I should be able to get you a copy. 73, Mike


----- Original Message ----- 
From: "ronnie.hull" <ronnie.hull at glowbugs.com>
To: "Mike Dorworth, K4XM" <k4xm at arczip.com>; "Discussion of AM Radio"
<amradio at mailman.qth.net>
Sent: Thursday, September 22, 2005 7:53 AM
Subject: Re: [AMRadio] Pi-Net vs Link Couple


>
> Mike I'm the fellow that is going to build up a Class C final using a
450TL.
> I would love to get a copy of that schematic for the 450TH rig in the
Editors
> and Engineers handbook. I have a few of those, but apparently, not that
one.
>
> I have a very nice B&W 850A or 852 that I can use in this rig. Either
should
> handle that tube fine, considering I'm not going to run much more than
2500
> volts on it anyway. Maybe 3000.
>
> I just got the worled biggest honker daddy plate transformer from W5OMR.
> 8200V center tapped ( 4100 - 0 - 4100 ) at 4.5KVA !!!  Yeah suh, takes 3
men
> and a dolly to move it!!
>
> This will be a fun project.
>
> 73's & batten down the hatches, here comes Rita..
>
> W5SUM
>
>
> ---------- Original Message -----------
> From: "Mike Dorworth,K4XM" <k4xm at arczip.com>
> To: "Discussion of AM Radio" <amradio at mailman.qth.net>
> Sent: Wed, 21 Sep 2005 23:10:59 -0400
> Subject: Re: [AMRadio] Pi-Net vs Link Couple
>
> > The Pi-Net will give a total of 50 db suppresion of harmonics. about
> > 20 in one spot and 30 in the other. Link couple can pass harmonics
> > to VHF by capacity coupling, hence the Faraday Shield Links used for
> > same later on. There is a nice single 450th Pi-Net rig shown in the
> > Editor and Engineers handbook. Also a couple of single ended ones in
> > the 1950 ARRL Handbook (for triodes).  Some triodes that require
> > lots and lots or drive can unbalance the grid tank, which is
> > required for triodes using Pi-Net. Lo capacity tubes like the 450th
> > is OK. The old timers mostly used tuners (antenna) and open wire
> > feeders to keep the harmonics down. Hazletine link neutralization
> > can also be used and no split tanks are needed in or out. Remember
> > Class C , which is required for Hi level AM, is a extreme distortion
> >  and harmonic generator so that some plan need to be in place to
> > handle the soup. Also a single band dipole is very frequency
> > selective and cuts way down on harmonics by itself. Multiband
> > dipoles, beams and multi dipole on one feeder and traps etc (G5RV)
> > are an open invitation to spread gook with only link output. Also
> > the guys that use CB lin years with no half wave filters get away in
> > mobile service without too many problems  due to the narrow
> > frequency discrimination of mobile antennas. Hope this helps, 73 Mike
> >
> > ----- Original Message ----- 
> > From: "Geoff" <w5omr at satx.rr.com>
> > To: "Discussion of AM Radio" <amradio at mailman.qth.net>
> > Sent: Wednesday, September 21, 2005 10:45 PM
> > Subject: [AMRadio] Pi-Net vs Link Couple
> >
> > > SO, here we are, well past 1991 and the 'law' that went into effect
> > > saying that 1,500w PEP output is the maximum RF Power output that we
> > > hams can run, regarldless of mode.  That doesn't deter the homebrewing
> > > spirit, but it does suggest that acheiving 1,500w PEP output is much
> > > easier than producing 1kW DC input to the final.  With the mindset of
> > > still wanting to use the classic high-level plate modulation scheme,
> > > engineering a rig to use only one tube in the final (a 4-250, 250TH,
> > > 304TH/TL, 4-400, etc), modulated by a pair seems to make more common
> > > sense.  That, and it's a bit more economic in filament requirements.
> > >
> > > I've heard recently that matching the output of the Class C
> > > pate-modulated final to the antenna is better, and more efficiently
> > > achieved by link coupling, vs Pi-Net.  On the other hand, it's argued
> > > that Pi-Net coupling produces less RFI than link coupling does.
> > >
> > > So, which is better?
> > >
> > > Why?
> > >
> > > What are the effects of nuetralizing a single tube in a balanced tank
> > > circuit?  If Pi-Net is to be used, does the final tube still need to
be
> > > nuetralized?
> > >
> > > I know of a guy who wants to build a rig using a single 450TL in the
> > > final, modulated by a pair.  He wants to pi-net the output, but I've
> > > heard that's a bad idea.
> > >
> > > I want to build a rig using a medium powered tride, perhaps a 250TH,
> > > modulated by a pair of 811's.  Pi-Net, or Link Couple?
> > >
> > > I like seeing this kind of technical discussion on the list.  I'm
> > > looking forward to all inputs.
> > >
> > > --
> > > 73 = Best Regards,
> > > -Geoff/W5OMR
> > >
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> >
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> ------- End of Original Message -------
>
>




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