[Amps] Class A for AM

[Tom W8JI]

>I agree.  It would seem that you shouldn't have to run so 
>conservative with
> push-pull to achieve the same or better linearity as a 
> single.  We know the
> even orders cancel.  Maybe some other unwanted effects 
> balance out too.
>
> Jeff/KA5MIR
>
> On Wednesday 15 November 2006 00:16, Bill L. Fuqua wrote:
>> I have wondered about that. There may be some 
>> improvement. During the time
>> that the single ended amplifier is approaching cutoff 
>> there is
>> considerable non-linearity. In a AB push-pull amplifier 
>> both tubes conduct
>> during through cross over and possibly improve the 
>> linearity. I wonder if
>> someone can put it to the test either  by simulation or 
>> by actually trying
>> it.

That does not apply to the AF signal content, or modulation. 
It only applies to the RF waveform and even-order distortion 
products of the RF signal. Push-pull cancels the even 
harmonic distortion of the RF signal. With a  7MHz  signal 
it cancels the 14 MHz harmonic (and other even harmonics). 
It doesn't do anything for splatter or odd-order distortion 
of information on the carrier.

Distortion of the audio and splatter is a result of the 
transfer function, or ratio of drive power to output power. 
Nothing else. Push-pull does not improve transfer function 
any more than a second tube in parallel would do. This is 
why linear BC transmitters don't bother with push-pull. 
(Transistor PA's often do, but the reason is most 
semiconductors cannot be paralleled easily for stability 
reasons. It isn't because of linearity or transfer 
function.)

73 Tom