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

[R.Measures]

On Jan 19, 2005, at 8:07 AM, Harold B. Mandel wrote:

> Dear Steve,
>
> Neutralization of tetrodes provides a better match between
> the driver and Power Amplifier, and also serves to protect
> the PA from deleterious oscillations.
>
> With the cost of a replacement tetrode weighed against
> the cost of materials, (inductor, capacitors, etc) of a
> neutralization circuit it almost seems effective to
> incorporate it in the design.
>
Amen, Hal.  After consulting a number of "amplifier experts" about my 
original 4cx5000A project -- a.k.a. Plywood Box #1), I was told that 
neutralization was not necessary with a Cag (feedback-C) of "only" 1pF. 
and a 450-ohm grid termination.   This turned out to not be the case, 
so I retrofitted a Bruene neutralization bridge, and revised my 
"experts" list.

cheers

> Hal Mandel
> W4HBM
>
>
>
>
>>
>> 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 ?
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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org