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

[Will Matney]

On Wed, 19 Jan 2005 07:43:09 -0800, R.Measures <r at 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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Will

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