[AMRadio] Pi-Net vs Link Couple


bcarling at cfl.rr.com bcarling at cfl.rr.com
Wed Sep 28 06:06:21 EDT 2005


ON another group they claim that you can get AT BEST 
35% efficiency with AM LInear mode with ANY class 
linear amplifier.

On 27 Sep 2005 at 9:32, John E. Coleman (ARS WA5BXO) wrote:

> I'll beat Don to the punch here.  
> 	Basically, high level modulation is the process of varying the
> supply voltage at an audio rate.  This process works properly as long as the
> ratio of plate current to plate voltage remains constant in the final.  The
> efficiency of the modulated final must remain constant over the range of
> variation, so that the output RF voltage follows the supply voltage.  Class
> C finals work best with this type of modulation and yes you can run a
> grounded grid final in class C.  It is very complicated to modulate it
> however.  The driver stage is part of the output in a GG circuit.  So it
> will need to be modulated as well.  The efficiency of a class C final is
> very dependent on the drive.  So modulating the driver affects the
> efficiency of the final over the modulation cycle.  It would be an extremely
> difficult task to get all the levels correct and compensate for the non
> linear modulation characteristics caused by having to modulate the driver.  
> 	GG is best left for linear operations.   
> 
> John, WA5BXO 
> 
> -----Original Message-----
> From: amradio-bounces at mailman.qth.net
> [mailto:amradio-bounces at mailman.qth.net] On Behalf Of bcarling at cfl.rr.com
> Sent: Tuesday, September 27, 2005 7:03 AM
> To: amradio at mailman.qth.net
> Subject: RE: [AMRadio] Pi-Net vs Link Couple
> 
> On 22 Sep 2005 at 20:20, Donald Chester wrote:
> 
> > A tube
> > with as much grid-plate capacitance as the 450TL or 250TH must be 
> > neutralised for proper operation, unless it is grounded grid.  Grounded
> > grid 
> > is not recommended for plate modulated finals.
> 
> For all tubes? Please explain...
> 
> 
> 
> 
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