On Wed, 19 Jan 2005 07:43:09 -0800, R.Measures <r@somis.org> wrote:
On Jan 19, 2005, at 7:11 AM, Steven J Fraasch wrote:
Has anyone successfully built a multi-band grid driven amplifier using a
4-1000 ?
If the control grid were swamped in the 50 to 200 ohm range, and the
Screen grid was made the shielding element (assume DC ground, and
cathode
and grid float DC), did you still experience instabilities such that
neutralization was required ?
Neutralization is useful because it reduces the input SWR to virtually
1:1 by canceling the grid-C, plus it makes the amplifier stable at the
operating frequency. However, neutralization has no effect on parasitic
oscillation.
Does anyone have a reasonably accurate SPICE model for the 4-1000 ?
The characteristic curves tell us that c. 140v peak is needed to
overcome the grid bias needed to obtain the proper ZSAC with 1000v on
the screen. For a 100w transceiver, a 200-ohm grid termination and
bifilar balun will deliver 140v-pk to the grid. RL is easy to figure
for whatever anode-V one is using. Who needs SPICE?
There was some mighty good equipment designed in the past using merely a
slide rule and a set of logarhithmic tables! Some with just the use of a
pencil and paper.
I am contemplating such a project to purge components.
The 4-1000 in GG doesn't have enough gain to warrant the project; I
would
use another tetrode such as a 4cx1500.
A 200w transceiver will drive a 4-1000A in g-g or an 8171 in grid-driven.
73, Steve K0SF
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Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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