Thats how I remember it also John but its been a long while since I read it!
BTW, when you mentioned the Tyler circuit in that 500KW amp what efficiency
improvement were you getting? What class and how is it driven?
Carl
KM1H
----- Original Message -----
From: "John Lyles" <jtml@losalamos.com>
To: <amps@contesting.com>
Sent: Tuesday, March 30, 2010 10:25 PM
Subject: [Amps] gg feedthru power
> In Eimac Amateur Service Newsletter AS-33, also in QST in June of 1967,
> Bill Orr and Bill Sayer (both at Eimac) state this:
> "Strictly speaking, the extra output power is not 'free', as r.f. power is
> expensive compared to d.c. plate power and may only be
> 'free' if it is unavoidably available. It is generally referred to as
> feed-through power, but the implication in this term may be
> misleading, as this portion of the drive power does not appear in the load
> circuit of the cathode-driven stage until after it is converted to a
> varying
> d.c. plate potential effectively in series with the main amplifier power
> supply. This converted drive power performs a useful function in class AB2
> and class B linear service by swamping out the undesirable effects of
> nonlinear grid loading and presenting a reasonably constant load to the
> exciter."
> (reference is made here to "SSB Principles and Practice", 1964 edition, by
> Pappenfus, Bruene. and Schoenike)
>
> Its a pretty good explanation of how it works. I think he means that the
> cathode to grid voltage swing from the driver is in series with the plate
> to grid voltage swing in the output. Since
> the cathode current and plate current are in the same path, with the
> slight difference being the grid current, it is essentially an increase in
> the plate voltage swing, with the same current, so that
> it appears as if the driver power is added to the output power. But there
> is no mechanism inside of the vacuum tube for RF to flow through and get
> from the input to the output, besides the
> effect of the electron beam which converts DC into RF at the fundamental
> frequency.
>
> Fun reading.
> 73
> John
> K5PRO
>
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