Output classes A and AB
 

On Oct 24, 5:44 am, Eeyore
wrote:
Patrick Turner wrote:
Eeyore wrote:
The definition of Class A is very simple. It requires that the output device(s)
never cease conducting under any signal condition.

It means slightly more than this because tubes don't cut off as sharply
as other devices.

I see what you're saying but I do believe that the definition is unchanged. Obviously
avoiding any region of significant non-linearity is preferable but that in its own right
doesn't change the definition.

Graham

Let's look at your definition again:

Poopie Stevenson wrote:
The definition of Class A is very simple. It requires that the output device(s)
never cease conducting under any signal condition.

Why don't you explain to us how a Class A amp can operate within the
class "under any signal condition", which presumably includes *much*
larger signals than the negative bias?

Your definition ipso facto makes Class A an impossible operating
condition because an increasing level of signal, permitted "under any
signal condition", will sooner or later drive the amp into cutoff. Of
course, long before then it will cease to be a high fidelity
amplifier, though, on the evidence of your posts, we don't expect that
to matter to you.

I repeat, a Class A amp, including that part of a Class AB amp
operating in Class A, are always and under any circumstances subject
to the designer's input signal limit or, if instead stated,
dissipation limit. To demand that a Class A amplifier work "under any
signal condition" is stupid for even a newbie, never mind someone like
you, Graham Stevenson, who claims to design electronic gear for sound
professional to use.

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

Output classes A and AB
 

On Oct 24, 10:48 am, John Byrns wrote:

Technically correct stuff snipped.

John:

I agree with what you say inasmuch as it is *absolutely* technically
correct. But the amplifier you posit is still a Class AB unit and/or a
unit that has been modified to make only Class A - and therefore NOT a
Class AB unit anymore - and as a 'modified' A not really all that hot-
sh*t an A either?

Point being that the GM V8 remains a V8 even though it is *capable* of
operating in 4 or 6 cylinder modes - albeit at much a much reduced PtW
ratio. And it could also be modified with a suitable network of
controls to remain in either 4 or 6 cylinder mode at all times - and
therefore *technically* be described as a 4 or a 6. It is certainly
not anyone's idea of a V8 anymore - nor what should be a good idea of
a 6 or 4.

Which, of course, would be a 100% marketing ploy, wouldn't it? To call
it a 4 or a 6 by virtue of the modifications?

As a purpose-built 4 or 6 would be a much better solution, wouldn't
it?

And that same purpose-built 4 or 6 could be made with the same
displacement, potential output HP and torque as a V8, couldn't it?

And that would, of course, cost a pretty penny - more than a similar
displacement & output V8? Large output Class A (tube) amps tend to be
costly, right?

So, an amplifier *may* operate in Class A mode for some range based on
its design. But it cannot, must not, nor should it be classified as a
Class A amp if it does not operate in Class A at all ranges.
Otherwise, what we have is a marketing ploy because as previously
stated: Class A = Good Class AB = Not So Good

All classes of amplifiers are equal, some are more equal than others.
Unless similar Orwellian terms apply, then the principle of the
excluded middle applies. Can't have it both ways.

I am not trying to be simplistic, just clear on what is meant and what
is implied. As things look from the discussion here, only Patrick is
discussing this with Douglas on equal terms. And I have a sense that
they agree more than they disagree. Andre has a bug up his butt - as
always - and therefore cannot discuss much of anything on any
reasonable terms. He really should step out of it and enjoy the
discussion as it is being pursued by his betters - I am certainly
watching it with interest. And the side issue of all this is that
between George, Bret and Andre, the atmosphere in this NG has been
pretty toxic of late. Maybe all three of them should take a rest and
let the air clear... although I do have my doubts as to George being a
discrete individual and not a sock-puppet.

Peter Wieck
Wyncote, PA

Output classes A and AB
 

In article .com,
Andre Jute wrote:

Historically, the original purpose of Class AB was to annihilate the
second harmonic which before made up such a very large part of the
THD, while still allowing beam tubes and pentodes to give much larger
power than available before.

Andre, why was Class AB necessary to annihilate the second harmonic,
didn't Push Pull operation already annihilate the second harmonic
irrespective of the class of operation?




The "invention" of Class AB as a hi-
fidelity amp is what spurred part of a Olsen's work on perception;
before it wasn't known that odd harmonics are proportionately much
more disturbing than even harmonics. It seems to me that AB amps with
largish parts of their output in Class A is a relatively modern trend,
possibly related to ever less-sensitive speakers.

I'm not sure I would agree with that, class AB amps were common even in
the days of efficient speakers, I don't see it as "a relatively modern
trend", if anything is a modern trend, I would think it is the return to
"pure" class A amplifiers on the part of many audiophiles.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

Output classes A and AB
 

In article .com,
Peter Wieck wrote:

On Oct 24, 10:48 am, John Byrns wrote:

Technically correct stuff snipped.

John:

I agree with what you say inasmuch as it is *absolutely* technically
correct. But the amplifier you posit is still a Class AB unit and/or a
unit that has been modified to make only Class A - and therefore NOT a
Class AB unit anymore - and as a 'modified' A not really all that hot-
sh*t an A either?

Point being that the GM V8 remains a V8 even though it is *capable* of
operating in 4 or 6 cylinder modes - albeit at much a much reduced PtW
ratio.

The GM 4-6-8 is not a good analogy because it has 8 cylinders even when
only 4 are operating. The class A vs. class AB amplifier is a different
situation because the only fundamental difference between the two is the
setting of the bias pot. If you ask nicely I might go in to some of the
non essential differences between the two.

I am not trying to be simplistic, just clear on what is meant and what
is implied. As things look from the discussion here, only Patrick is
discussing this with Douglas on equal terms.

I wouldn't put Douglas, a.k.a. Multi-grid, on equal terms with Patrick.

And the side issue of all this is that
between George, Bret and Andre, the atmosphere in this NG has been
pretty toxic of late. Maybe all three of them should take a rest and
let the air clear... although I do have my doubts as to George being a
discrete individual and not a sock-puppet.

Who is "George", I haven't noticed anyone, "discrete individual" or
"sock-puppet", by that name participating in this discussion?


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

Output classes A and AB
 

On Oct 23, 6:51 pm, John Byrns wrote:
In article . com,

Multi-grid wrote:
On Oct 24, 1:37 am, Andre Jute wrote:

As for Dougles Multi-grid's silly insistence that signal and
dissipation have nothing to do with Class A operation, thanks for the
giggle, sonny, but you'd better hit the books lots more before you
seek entry to this club.

They don't Andre, no matter how much you claim they do. Class A, is as
simple as you first stated it:

***Class A operating conditions do not permit the output device to
cease conducting.***

Precisely, that is why when the operating conditions of a class AB
amplifier are restricted by limiting the applied input voltage the
amplifier is able to put out class A power at a level that is lower than
the maximum available class AB power.

It should get the addition that remote cut off behaviour is not
included.

Most real world tubes display remote cut off behaviour as the plate
curves become distinctly compressed in the high voltage low current
quadrant. I guess that rules out the possibility of any tube amplifier
operating class A.

In the halflight dreamworld inhabited by Dougles Zero-sound, Poopie
Stevenson and Worthless Wiecky, SE amps would be impossible, Class A1
amps would be impossible, and all other classes would produce zero
music -- in fact all other classes would produce 100 per cent pure
noise by being operated at all sonic peaks at either max current and
zero voltage or zero current and voltage plate overvoltage. All of
that follows logically from Poopie's absurd redefinition of Class A as
a Class in which "the output device(s)never cease conducting *under
any signal condition*," (emphasis added). It's ludicrous. Any amp can
be driven out of class by excessive signal voltage. That clown Poopie
Stevenson has overreached himself again; Dougles Multi-grid is an
ignorant (and impertinent) troll of a kind well known on RAT; poor
Witless Wiecky is just another know-nothing garage trader who wantst
to move up to repair hack status.

This whole affair is nuts. We're wasting our time arguing with people
who will say anything to put someone down, regardless of the known
facts of physics. I've always known that Poopie and Worthless are
ineducable on any timescale less than glacial. Dougles Zero-sound is
clearly another veeeeery sloooow learner. The stubborn lack of
sophistication in his ignorance makes me nostalgic for Pasternack, who
at least sometimes said something interesting as he twisted this way
and that in the web of his lies; at the very least Plod never would
have been dumb enough to attempt lying about something as simple as
operating classes.

Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

One has to laugh. The alternative is unthinkable...

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

Output classes A and AB
 

John:

Please note the interpolations:

On Oct 24, 1:53 pm, John Byrns wrote:

The GM 4-6-8 is not a good analogy because it has 8 cylinders even when
only 4 are operating. The class A vs. class AB amplifier is a different
situation because the only fundamental difference between the two is the
setting of the bias pot. If you ask nicely I might go in to some of the
non essential differences between the two.

Mpffff... of course. But you postulated the series of zeners and so
forth so as to make an as-designed AB into a pure Class A amp. From
that, all else follows. Many things can be done - the question is
whether they should be done to that amp and if done would the results
be better/worse/as-good as if purpose-designed from the ground up.
Otherwise, one is forcing the proverbial square peg into the legendary
round hole.

I wouldn't put Douglas, a.k.a. Multi-grid, on equal terms with Patrick.

Discussing on equal terms - not necessarily on equal terms overall.

Who is "George", I haven't noticed anyone, "discrete individual" or
"sock-puppet", by that name participating in this discussion?

Middius, and not necessarily in this discussion, but certainly part of
the general miasma.

Fly poop on the right, pepper on the left.

Peter Wieck
Wyncote, PA

Output classes A and AB
 

John Byrns wrote:

Andre Jute wrote:

Historically, the original purpose of Class AB was to annihilate the
second harmonic which before made up such a very large part of the
THD, while still allowing beam tubes and pentodes to give much larger
power than available before.

Andre, why was Class AB necessary to annihilate the second harmonic,
didn't Push Pull operation already annihilate the second harmonic
irrespective of the class of operation?

Yes, you are right. It does.

The SOLE purpose of AB is to produce larger power outputs using the same tubes.
The dissipation in the output tubes is very considerably lower than that in
Class A.

Graham

Output classes A and AB
 

Andre Jute wrote:

In the halflight dreamworld inhabited by Dougles Zero-sound, Poopie
Stevenson and Worthless Wiecky, SE amps would be impossible, Class A1
amps would be impossible, and all other classes would produce zero
music -- in fact all other classes would produce 100 per cent pure
noise by being operated at all sonic peaks at either max current and
zero voltage or zero current and voltage plate overvoltage. All of
that follows logically from Poopie's absurd redefinition of Class A as
a Class in which "the output device(s)never cease conducting *under
any signal condition*," (emphasis added). It's ludicrous.

It's actually the only accurate definition.


Any amp can be driven out of class by excessive signal voltage.

Overdriving to cut-off is merely gross abuse and a complete red herring /
irrelevance.

You really should constrain yourself to talkind about stuff you understand.
Which would seem not to be very much going by your posting history.

Graham

Output classes A and AB
 

flipper wrote:

Eeyore wrote:
Andre Jute wrote:

In the halflight dreamworld inhabited by Dougles Zero-sound, Poopie
Stevenson and Worthless Wiecky, SE amps would be impossible, Class A1
amps would be impossible, and all other classes would produce zero
music -- in fact all other classes would produce 100 per cent pure
noise by being operated at all sonic peaks at either max current and
zero voltage or zero current and voltage plate overvoltage. All of
that follows logically from Poopie's absurd redefinition of Class A as
a Class in which "the output device(s)never cease conducting *under
any signal condition*," (emphasis added). It's ludicrous.

It's actually the only accurate definition.

Any amp can be driven out of class by excessive signal voltage.

Overdriving to cut-off is merely gross abuse and a complete red herring /
irrelevance.

It's not a 'red herring' when you clearly stated "under any signal
condition."

Do you normally operate amplifiers into gross distortion ? I was trying to avoid
the '360 degree' terminology which kind of implies for its part, sinewave only
use.

Do please, if you desire, change it to 'any valid signal condition for which the
amplifer is rated'.

Graham

Output classes A and AB
 

On Oct 24, 6:29 pm, Andre Jute wrote:




Historically, the original purpose of Class AB was to annihilate the
second harmonic which before made up such a very large part of the
THD, while still allowing beam tubes and pentodes to give much larger
power than available before. .






- Show quoted text -

Well Andre, you've stepped in it this time...:) AB operation cannot
effectively cancell *ANYTHING*.

Odd sums anyway.

Not second HD( or the even of any order ) because each phase is biased
where the characteristics are changing too rapidly with plate current.
This is the rest of the Class A definition that is implied, the finals
are biased so that the change in characteristic for the opposing
phases approximately cancells( and thus the even HD ). It is why the
AB amp can't be labled A while both phases of the finals are
conducting( or that that single definition is not enough to describe
Class A ).

The x power in A, and XXX power in AB is just serving notice that
marketing had its way with the ad copy.

AB was an obvious means of minimizing cross-over distortion and
maximizing power. It works just as well for directly heated triodes
with no NFB as it does for pentodes like the KT88 running a lot of
it...:)
cheers,
Douglas