[AMRadio] Max power off from plate current dip problem 32v1...

[Gary Schafer]

If the max output does not occur at plate current minimum then the final is not
properly neutralized. Seems I remember reading somewhere that it is important for
an AM transmitter to be properly neutralized for best modulation too.

Screen current should peak with plate current dip. Grid current should peak also
and you should get max output when all these things happen.

By the way the above is true except for any amplifier that has negative rf
feedback, like the Collins S line equipment. In that equipment when the
neutralization and feed back neutralization are properly set up the max output
will occur with plate current dip and the grid current will also dip! Just the
opposite of a non feed back amp.  The reason that happens is at plate current dip
and max output, there is more voltage being fed back to the grid circuit (out of
phase) that reduces the drive.

Screen current peak is a better indicator of resonance than the plate current
dip. It is very sensitive compared to the plate dip.

Some DX 100's have neutralization added to them. When neutralized properly you
may find the grid drive marginal on 10 meters. I had asked several others with
DX100's how much grid current they could get on 10 meters and it usually seemed
to be more than I could get. It finally dawned on me that they probably did not
have the neutralization in their units.
Without neutralization the DX100 has enough positive feed back to make it look
like there is lots of drive but it is really on the verge of taking off.

73
Gary  K4FMX


Larry Szendrei wrote:

> I concur with Steve - Most if not all my tube transmitters show max.
> power out off the plate current minimum. I wouldn't lose any sleep over
> it, but if the final is taking off on its own, something (such as
> neutralization, if that's the cause) needs to be done.
>
> I remember reading somewhere that the screen current minimum is a better
> indication of resonance than the plate current minimum in a tetrode
> calss-C amp - that would seem to imply that the plate current dip will
> -not- coincide with max output for this case.
>
> 73,
> -Larry/NE1S
>
> W2ZR at aol.com wrote:
> >
> >         <mailto:amradio-request at mailman.qth.net?subject=unsubscribe>
> > List-Archive: <http://mailman.qth.net/pipermail/amradio/>
> > Date: Mon, 24 Jun 2002 20:09:43 EDT
> >
> > Hi,
> >        I don't think I've ever tuned a rig where maximum output occurred at
> > the same point as the plate current dip.
> >
> > 73,
> > Steve W2ZR
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