>
>> We know that negative feedback in audio amplifiers improves linearity and
>> reduces distortion. What would it take to improve RF linears with
>> feedback? In thinking about it for a bit (not enough time, no doubt). It
>> seems that RF feedback will introduce lots of problems with stability
>> because the feedback will vary in phase over frequency...producing an
>> oscillator. Linearizing the envelop might improve things, but it doesn't
>> do anything about the phase component...might even worsen it.
>
>Grounded grid amplifiers already have a very high level of almost
>perfect negative feedback as long as the grid is properly grounded.
>
>Some tubes have long grid leads that add some amount of
>uncontrolled feedback, and some amplifiers add some uncontrolled
>feedback through intentional "floating" of the control grid through
>low value capacitors.
>
>> In the commercial world, broadband, low IMD amplifiers use feed forward
>> techniques...precompensate the input to produce a clean output. The
>> principle seems clear but how it applies to a bandswitched amp and how a
>> ham with just a grid dipper can set it up seems murky.
>
>You can add negative feedback to a grid driven tetrode with the
>addition of an unbypassed resistor in the cathode.
>
True enough. However, with a grid-driven tetrode, cathode R subtracts
from the cathode/screen potential on voice peaks, so R must be kept
fairly low.
Eimac recommends 11-ohms of Rc for the 4CX600JA. A cathode feedback R is
ideal for g-g config.
>
cheers
end
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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