[Amps] Re: AB1 v. AB2

[Rich]

>
>----- 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:
>> >> 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?


-  Rich..., 805.386.3734, www.vcnet.com/measures.