He is doing an analysis of the circuit. Particularly the transfer function
between the plate and the grid.
To do this you have to look at the internal impedances of the tube itself.
There is capacitance between the
plate and grid, and capacitance between the grid and cathode and a "vacuum
tube" diode between the
grid and cathode. The real part of the impedance between the grid and cathode
(the diode) is a function of the
grid current, due to the electrons going between the cathode and the grid. At
zero grid current the real part of this
impedance is infinite. The capacitance is still there. and so on. Anyway he is
looking at the phase relationships between
the AC plate voltage and the AC grid current. And it changes with grid current.
etc.
73
Bill wa4lav
________________________________________
From: amps-bounces@contesting.com [amps-bounces@contesting.com] On Behalf Of
TexasRF@aol.com [TexasRF@aol.com]
Sent: Wednesday, August 26, 2009 9:52 PM
To: dezrat1242@yahoo.com; amps@contesting.com
Subject: Re: [Amps] RF parts and parasitics!!
When the grid is grounded for cathode driven operation is there a
difference between cathode to grid impedance and cathode to ground impedance?
Doesn't seem there would be.
73,
K5GW
In a message dated 8/26/2009 7:59:38 P.M. Central Daylight Time,
dezrat1242@yahoo.com writes:
ORIGINAL MESSAGE:
On Wed, 26 Aug 2009 20:09:40 -0400, "Carl" <km1h@jeremy.mv.com> wrote:
>
>I fail to see the phrase "very high" anywhere in that article.
>
>Perhaps you can assist these tired old eyes.
REPLY:
My tired old eyes read his statement "When grid current is absent, the
grid-to-cathode impedance is nearly an open circuit" and paraphrased that
as
"very high". Did I err?
73, Bill W6WRT
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