amps-request@contesting.com wrote:
>
>
> Message: 8
> To: amps@contesting.com
> Reply-To: ad5gb@myway.com
> From: "ad5gb" <ad5gb@myway.com>
> Cc:
To: <amps@contesting.com>
> Date: Thu, 28 Nov 2002 22:18:13 -0500 (EST)
> Subject: [Amps] AB1 vs AB2 ???
>
> Greetings Amps gurus,
>
> Happy Holidays and special thanks to all who've been so helpful to me over
> the past year! It means a great deal to me.
>
> I'm wondering if someone can explain why AB2 GG service is more linear than
> AB2 grid-driven service?
I dunno about that one... check a handbook.
> I've been working with my latest project ( still on paper ) which is a pair
> of 4-400As and it appears that all other things being equal, about 200-250
> watts more is available in AB2 operation than is available in AB1.
This is because in effect the load line is "longer" in AB2 than AB1. AB2
permits you to draw grid current, whereas
AB1 does not. That means you can drive the grid *positive* past "0" whereas in
AB1 your drive stops at "0"
since current can not be delivered to the grid in AB1.
> I guess I understand why this is but don't quite understand why AB2
> grid-driven service gives poor linearity yet AB2 cathode-driven service is
> acceptable.
Not sure that it does.
>
>
> I decided to try grid driven service because it simplifies bandswitching (
> given the parts in my junkbox ) and in passive configuration, makes for
> construction simplicity ( no tuned input needed ).
Actually, it's not any different. Plenty of amps have been built without a
tuned input. Of course, a tuned
input is a good idea for best operation. Assuming something like a xcvr with a
tuner built in it might not
make all that much difference, since the built in tuner acts quite a bit like
the tuned input stage in the amp,
maybe even better since it is likely higher Q. The amp input is lower Q in
order to get enough bandwidth.
I guess you can use a smaller switch at the input - but that's not a terribly
good reason to base an
amp design upon.
>
>
> Again.... many thanks to all and Happy Holidays
>
> RD
>
Of course, I could be wrong... :- )
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