[Amps] RF parts and parasitics!!

[Fuqua, Bill L]

  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 at contesting.com [amps-bounces at contesting.com] On Behalf Of TexasRF at aol.com [TexasRF at aol.com]
Sent: Wednesday, August 26, 2009 9:52 PM
To: dezrat1242 at yahoo.com; amps at 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 at yahoo.com writes:

ORIGINAL  MESSAGE:

On Wed, 26 Aug 2009 20:09:40 -0400, "Carl"  <km1h at 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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