>> >Can anyone help me with copies of the following articles. I'm having
>> >trouble finding them locally.
>> >
>> >cheers, Paul
>
>> This is an article I missed, Paul.
>> However, the article should be interesting because the grid's DC bias
>> voltage in a Class AB1 amplifier is normally adjusted so that, with
>> full-throttle grid drive, the grid draws ZERO grid current. This means
>> that the exciter can not overdrive the Class AB1 tetrode (or pentode)
>> into the distortion-producing grid current region Thus, ALC is not only
>> not necessary, similar results could be achieved by turning down the
>> microphone gain AFTER the amplifier is tuned up under maximum signal
>> conditions.
>
>That's not necessarily correct data. Exciter's power capabilities as
>well as the PA's grid circuit efficiency varies from band to
>band, plus someone is likely to eventually connect a different radio
>to the PA
True
This is why the first tuneup step is to adjust the grid bias V so that
the grid is drawing ZERO grid current with maximum drive applied. This
happens before the anode and screen voltages are applied. (interested in
the complete AB1 tuneup procedure? See
*Amplifiers* at <http://www.vcnet.com/measures>)
>While Rich's statement is correct IF the PA is designed and adjusted
>to NEVER draw grid current, that's an almost impossible situation to
>find in the real world.
...snip...
I have never seen a Class AB1 amplifier design that does not have
adjustable grid bias voltage.
A Class AB1 PA is not designed to NEVER draw grid current. It is
designed so that the grid bias V can be ADJUSTED to zero grid current for
the specific drive level being applied.
>In the practical world, ALC is actually MORE necessary in a class AB1
>PA. ...
...SNIP...
And remember boys and girls: it's really not a very good idea to claim
that you are an "expert". :)
Rich---
R. L. Measures, 805-386-3734, AG6K
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|