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
>
>
>
> - Rich..., 805.386.3734, www.vcnet.com/measures.
--
_-_-bearlabs
http://www.bearlabsUSA.com
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