Push pull is necessary in a class B audio amplifier because the second tube
makes up for the missing half cycle of the first tube. With only one tube in
a class B audio amplifier the output would be half of a sin wave.
In an RF amplifier the tank circuit is high enough Q so that it makes up the
other half of the sin wave with a single tube class B amplifier.
The only difference in the RF output waveform between push pull and a single
tube is that the push pull circuit has less RF second harmonic energy.
73
Gary K4FMX
> -----Original Message-----
> From: Bill L. Fuqua [mailto:wlfuqu00@uky.edu]
> Sent: Wednesday, November 15, 2006 12:17 AM
> To: garyschafer@comcast.net
> Cc: amps@contesting.com
> Subject: Re: Re: [Amps] Class A for AM
>
> 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.
>
> 73
> Bill wa4lav
>
>
> -----Original Message-----
> From: "Gary Schafer" <garyschafer@comcast.net>
> To: <amps@contesting.com>
> Date: Tue, 14 Nov 2006 22:26:36 -0600
> Subject: Re: [Amps] Class A for AM
>
> No. Push pull has nothing to do with amplitude linearity in RF service.
>
> 73
> Gary K4FMX
>
> > -----Original Message-----
> > From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
> On
> > Behalf Of Robert B. Bonner
> > Sent: Tuesday, November 14, 2006 8:16 PM
> > To: 'Tom W8JI'; 'Gary Schafer'; 'KA5MIR'; amps@contesting.com
> > Subject: Re: [Amps] Class A for AM
> >
> > Hey Tom, isn't that why they went to PUSH PULL finals with a link
> coupled
> > output? Still simulates class A with a pair of class B finals...
> >
> > I think a couple nice 4-1000's glowing in the rack should just about do
> > it.
> >
> > Modulate it anyway you'd like. Sometimes just sometimes the old way is
> > the
> > best way.
> >
> > I wonder if I could still build a link coupled final? The last time I
> did
> > one was my second novice transmitter a little 6DQ6 25 watter.
> >
> > 4-1000's? Whoops the only things I have pairs of here are: 3-500's
> 8877's
> > 3CX3000's and YC-156's drat fresh outta 4-1000's.. Oh and you guys had
> me
> > all excited there for a minute.
> >
> > BOB DD
> >
> > -----Original Message-----
> > From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
> On
> > Behalf Of Tom W8JI
> > Sent: Tuesday, November 14, 2006 8:06 PM
> > To: Gary Schafer; 'KA5MIR'; amps@contesting.com
> > Subject: Re: [Amps] Class A for AM
> >
> > > Except in class A the input power never changes. If it is
> > > set up for 6000
> > > watts input in order to provide 1500 watts output @25%
> > > efficiency then the
> > > input power will always be a constant 6000 watts with or
> > > without modulation
> > > or carrier.
> > >
> > > When it is putting out 375 watts carrier the input power
> > > will still be 6000
> > > watts.
> > >
> > > So the dissipation would be 6000 watts minus power out for
> > > any given output
> > > power.
> >
> >
> > That's the way I see it also.
> >
> > Since it should make around 50% on peaks it should make
> > around 25% on carrier, and 3000 watts plus headroom of
> > standing power should do it.
> > It will just be useful output power minus standing zero
> > signal dissipation.
> >
> > 73 Tom
> >
> >
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> >
> >
> >
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>
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