>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
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