[Amps] RF parts and parasitics!!

[Alex Eban]

It does make a big difference!
By convention' all impedances are measured from the electrode to ground
The grid impedance is actually very high and mostly capacitive, as long as
you don't draw grid current. With grid current it is about equal to the grid
voltage divided by the current measured-more or less.
In GG, the input impedance is approximately the load resistance divided by
the tube's transconductance, very approximately and it's mostly resistive:
that's why it absorbs power from the driver.
The element common to both the input and the output is considered to be
grounded- the grid in our case- so any measurement referred to it is
actually referred to ground, not the grid. So, the grid to cathode impedance
is a non existing entity.
Alex	4Z5KS

-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of TexasRF at aol.com
Sent: Thursday, August 27, 2009 4:52 AM
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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