On Jan 9, 2006, at 12:56 PM, Jim Kearman wrote:
>
>> Loading an amplifier heavier than where maximum output occurs helps to
>> keep the operating region in the more linear portion of the load line.
>> In other words heavier loading helps keep the operation down below the
>> upper curve of the load line where flat topping starts to occur, but
>> at
>> the expense of some efficiency.
>
> Thanks. If I understand correctly, loading more heavily presents a
> lower impedance to the anode(s), and also incidentally reduces network
> Q.
** Q's essentially the same. Jim. Loading heavier keeps the
instantaneous anode potential from dipping down into the non-linear
region of the tube where anode-current is max. On the characteristic
curves, this is the area at the left where the flat lines begin to bend
-- and that's where distortion begins.
> As a CW op, my main concern is efficiency and minimizing harmonics. It
> was difficult for me to feel confident that I was correctly
> calculating the required load impedance for my 4CX800As. Now I see
> that by making the load C large enough, I'll have the flexibility to
> match a wide range of plate Zs while maintaining adequate network Q.
> Having enough loading C only becomes a problem on 80 and 160, but this
> amp will be used only on 160-80-40, so getting those numbers right was
> critical.
>
> 73,
>
> Jim, KR1S
> http://kr1s.kearman.com/
>
>
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>
>
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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