[AMRadio] Pi-Net vs Link Couple


Barrie Smith barrie at centric.net
Thu Sep 22 22:31:46 EDT 2005


----- Original Message ----- 
From: "Mike Sawyer" <w3slk at uplink.net>
To: "Discussion of AM Radio" <amradio at mailman.qth.net>
Sent: Thursday, September 22, 2005 5:17 PM
Subject: Re: [AMRadio] Pi-Net vs Link Couple


> Doesn't the BC-610 accomplish this with the 250TH?  Yes.

 Or might it be that it is
> utilizing half the coil.  No.
> Mike(y)
> W3SLK
> ----- Original Message ----- 
> From: "Brett gazdzinski" <Brett.gazdzinski at mci.com>
> To: "'Discussion of AM Radio'" <amradio at mailman.qth.net>
> Sent: Thursday, September 22, 2005 8:13 AM
> Subject: RE: [AMRadio] Pi-Net vs Link Couple
>
>
> I don't think there is any way to run a triode single ended with link
> coupled
> output, not in class C.
>
> I run a pair of 812A's (or 811A's, or V70D's) push pull link coupled 
> output
> modulated by a pair of 811A's.
> It works very well.
>
> You can run them up to 2000 volts on the plates, or 1750, 0r 1500.
>
> I can get 400 watts carrier out pushing them, 350 watts out has the tubes
> showing no color.
>
> That is very close to the legal limit with plenty of audio.
>
> The 812/811 tubes are cheap, work from 1000 to 2000 volts, and
> don't take up a lot of space.
>
> I used small vacuum variable caps for neutralization, kilowatt
> coils, and a 6000 volt plate tuning cap.
> I got the small (2 to 30 pf @30,000 volts) neut caps out of old paging
> transmitters someone gave me, they ran a 4-400 at 3000 volts on 70? MHZ.
>
> Brett
> N2DTS
>
>
>
>
>
>
> -----Original Message-----
> From: amradio-bounces at mailman.qth.net
> [mailto:amradio-bounces at mailman.qth.net] On Behalf Of Geoff
> Sent: Wednesday, September 21, 2005 10:46 PM
> To: Discussion of AM Radio
> 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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