----- Original Message -----
From: Rich <2@vc.net>
To: <bearlabs@netzero.net>; AMPS <amps@contesting.com>
Sent: Friday, November 29, 2002 1:40 PM
Subject: Re: [Amps] Re: AB1 v. AB2
>
>
> >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.
> >
> ** AB2 doesn't permit anything. AB2 neans the operator Chose to drive
> the tube into its less-linear grid-current region. Up until that point,
> the tube is operating partly in Class A and then in Class AB1 -- as the
> grid-V sinusoidally decreases as it approaches 0V .
By *definition* AB2 means that the grid is driven positive with respect to
the cathode - and regardless *is* in the grid current region. AB1 by
definition is up to
"0" volts with respect to the cathode, and NEVER draws any grid current.
An amp set up for AB1 can NOT be driven into grid current - if it is able to
be
driven into grid current then it is an AB2 amplifier, regardless of how you
chose
to run the input levels.
In the case of most circuits, the AB1 amps are AC coupled and the AB2 amps
are
DC coupled to the grids - which permits current to flow. This is especially
clear
in audio applications...
You can *say* that an amp is "in" AB1 until it recieves a signal that drives
it into
grid current, but I don't know of anyone that can control peaks that well.
So, ultimately
the difference in how an amp is classified is not where you run it, but
*how* it is
designed.
_-_-bear
> > _-_-bear
>
>
> - Rich..., 805.386.3734, www.vcnet.com/measures.
>
>
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