BEAR wrote:
> Rich wrote:
>
> > >
> > >----- 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.
> > >
> > ** increase drive to the point that grid current flows and the AB1 amp
> > becomes an AB2 amp.
> >
> > >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...
> > >
> > ** with AC coupling, grid-current flows into the grid bias supply.
> >
> > >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.
> >
> > ** so increasing drive will not eventually cause grid current in a well
> > designed AB1 amp?
>
> it can't. If it can then it is an AB2 amp.
>
> _-_-bear WB2GCR
>
So how would you "design an AB1 amp that could never go into grid current" with
increased drive?
73
Gary K4FMX
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