They way I read it is that a tube that requires higher drive absorbs more of
the drive power, less power to feed thru, and results in more negative
feedback. The more negative feedback the lower the IMD.
His statement was that a 10:1 ratio of drive power to feed thru power would
be optimum and result in low IMD.
I don't think that he describes that as being reality though.
The driver is actually in series with the final tube. So the plate waveform
acts to modify the driver waveform which results in the feedback.
As I remember the way the old power rule read it was: the plate input power
of all stages delivering power to the antenna must not exceed 1 kw. So this
meant that if some of the driver power is fed thru the amp to the antenna
then the power input of the driver must be considered as delivering power to
the antenna as well as the final amp stage.
There was no mention of how much the driver power accounted for the total
power but only that its input power must be added in to the total.
73
Gary K4FMX
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
> On Behalf Of Roger
> Sent: Tuesday, March 30, 2010 8:27 PM
> To: Carl
> Cc: amps@contesting.com; TexasRF@aol.com
> Subject: Re: [Amps] gg feed through power
>
>
>
> Carl wrote:
> > Trying to decipher Orr at times is a task.
> >
> > Is he trying to say that the tube absorbs 90% and feed thru 10%?
> >
> If true that only 10% is fed through it would make the old FCC reg about
> adding the driving power to the output a bit strange as it seems as I
> recall we were expected to add the driving power to the input power of
> the amp when computing the legal 1KW DC input, or 2 KW PEP.
>
> As the driving power goes into the cathode which is in phase with the
> plate power output, I'd expect the majority of that power to show up
> minus perhaps the grid power or am I looking at that wrong?
>
> 73
>
> Roger (K8RI)
> > If so wouldnt loading for optimum grid current in the spec sheet
> accomplish
> > that? Sort of by default?
> >
> > Ive never read that version, which edition were you reading?
> >
> > Carl
> > KM1H
> >
> >
> >
> > ----- Original Message -----
> > From: <TexasRF@aol.com>
> > To: <amps@contesting.com>
> > Sent: Tuesday, March 30, 2010 7:13 PM
> > Subject: [Amps] gg feed through power
> >
> >
> >
> >> After more reading in the Orr book, I discovered a discussion of feed
> >> through power in a cathode driven amplifier.
> >>
> >> We have all heard about the drive power adding to the output power.
> Orr
> >> says, and I am paraphrasing here, that a PORTION of the drive power
> is
> >> added
> >> to the output power. He goes on to say that the greater the ratio of
> >> drive
> >> power to the feed through power, the better the imd performance. He
> >> further
> >> suggested that the optimum feed through power for best imd
> performance is
> >> about 10%.
> >>
> >> Heck, 10% of a 100w drive level is insignificant and might as well be
> >> ignored.
> >>
> >> He did not describe how one goes about attaining the 10% feed through
> >> level
> >> and I suspect there is no control of this. Perhaps you get what you
> get
> >> with a given tube?
> >>
> >> He also wrote about the improved imd performance due to the heavy
> negative
> >> feed back inherent in cathode driven amplifiers compared to grid
> driven;
> >> often in the 10 to 15 dB range of improvement.
> >>
> >> We have always heard this to be so; at least that old saying is
> correct.
> >>
> >> 73,
> >> Gerald K5GW
> >>
> >>
> >>
> >>
> >>
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> >>
> >
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> >
> >
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