Doherty Amplifier

[Andre Kesteloot]

Bob,
thanks for the clarifications on the Doherty amplifier.
The RCA approach, named by them the "Ampliphase" sold fairly well in the 
AM (medium wave band), as I recall, but as I mentioned earlier, much to 
tricky in the HF band, where multiple QSY every night would often be 
necessary.
Its great advantage was the fact that one did not have to produce a huge 
amount of Audio power to modulate the output stage, and yet audio 
quality could, be quite good. Hence one gained in power consumption, 
rack space, modulation transformers, etc. Maintenance was therefore easier
73
André

****************************

Bob Bruhns wrote:
> Hi Andre,
>
> I don't know if anyone sold a Taylor system transmitter.  The Taylor system was almost a "lost ark" in the AM community - people
> kept asking about it, but the knowledge was lost, until someone gave me the right hint, and I found that patent.
>
> There is a series-modulator system that is basically similar, but it does the trick at baseband, and provides modulated B+ to a
> regular Class-C modulated stage.  You would think that this would have been used back in the old days, but the references I see are
> recent.  One series device, a tube or a transistor, provides B+ from a supply that is a little higher than the unmodulated B+ level.
> This device normally operates just below saturation, and it works as a series element that can reduce the voltage from there.  With
> no modulation, it drops the voltage just a little bit to the unmodulated B+ level,  and this device handles the negative modulation
> peaks.
>
> A second device goes to a higher voltage supply, about 2.5 the unmodulated B+ level, or a litle higher.  This device is running
> almost cut off.  When it is driven into conduction, it can raise the modulated B+ to 2X the unmodulated level or a bit higher.  This
> device handles the positive peaks.
>
> Efficiency is reasonably high at carrier level, dropping somewhat with modulation, but no big audio transformers or inductors are
> required, and no special multi-tapped RF section is required either.  I have seen this system called a 'class-B series modulator'.
> It is sometimes used for AM using transistors operating around the 50V level, to modulate solid-state class E RF amplifiers.
>
> www.amfone.net/21stAM/class_b_series.htm
>
>    Bob, WA3WDR
>
>
> ----- Original Message ----- 
> From: "Andre Kesteloot" <andre.kesteloot at verizon.net>
> To: "Bob Bruhns" <bbruhns at erols.com>
> Cc: "AMRAD Tacos" <tacos at amrad.org>
> Sent: Wednesday, August 08, 2007 10:31 PM
> Subject: Re: Doherty Amplifier
>
>
>
>
> Bob Bruhns wrote:
>   
>> An interesting alternative is the Taylor linear amplifier.
>>
>>     
> Bob
> thanks for the pointer
> do you know who, if anyone, marketed this invention ?
> 73
> André N4ICK
>   
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>   
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