Re: [Amps] Grid driven Multi-band amp using 4-1000

[R.Measures <r@somis.org>]

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?
> 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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