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Re: [Amps] 4-1000A in Passive grid-driven use?

To: wlfuqu00@uky.edu
Subject: Re: [Amps] 4-1000A in Passive grid-driven use?
From: R.Measures <r@somis.org>
Date: Fri, 30 Apr 2004 08:01:06 -0700
List-post: <mailto:amps@contesting.com>

On Apr 30, 2004, at 6:32 AM, Bill L. Fuqua wrote:



I don't know if anyone has actually made a cathode driven biased 4-1000A AB1 amplifier but it should be very low in distortion compared to either zero bias grounded grid or common cathode operation. That is because of the fact that there would be very little grid current

ï AB1 means there is zero grid-current. AB2 means there is some grid-current.


and the plate RF current would be the same as the drive RF current and the power gain would come from the ratio of cathode drive impedance and plate impedance. If the plate impedance was 5000 ohms and drive impedance 200 ohms then the power gain would be 25 or so.

ï Since there is zero signal potential applied between the grid and the cathode, the power gain of a Class AB1 / "super cathode driven"stage is roughly the grid-screen amplification factor -- which is typically 4 to 6 in most tetrodes.


It would be interesting to try. I expect that the cahtode impedance would be somewhere between 100 and 200 ohms. It should be somewhat greater that gg due to the greately reduced grid current.
And just about all of your drive power would pass thru to the output.

ï Agreed, Bill. cheerz

73 Bill wa4lav

73
Bill wa4lav
-----Original Message-----
From: "R.Measures" <r@somis.org>
To: n7ioh <n7ioh@cybertrails.com>
Date: Wed, 28 Apr 2004 20:39:43 -0700
Subject: Re: [Amps] 4-1000A in Passive grid-driven use?


On Apr 28, 2004, at 12:38 PM, n7ioh wrote:


   Are there any problems in using the 4-1000A in a passive
grid-driven mode on 160 - 10 meter or on 6 meters?

ï Above 30m, it's a good idea to tune out the grid's XC. See: http://www.somis.org/D_a_05.GIF The XL of L1 tunes out the grid's XC for whatever frequency you choose. note -- this is the first step in tuning up such a machine. .

If not, what kind of output can I expect to get?

ï Depends on anode V and screen V. With 7kV and 1kV, you should be able to get 2.6 out.

Second, I have seen amps that use a roller inductor and not a band
switch, any thoughts?

ï They provide the best match over a wide frequency range.


Richard L. Measures, AG6K, 805.386.3734. www.somis.org

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Richard L. Measures, AG6K, 805.386.3734. www.somis.org

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