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 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. 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.
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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