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Peter Wieck Peter Wieck is offline
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Default 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



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John Byrns John Byrns is offline
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Default 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

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Default 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

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Default 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


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Default 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



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Default 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

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Default 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

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Default 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

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Default 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

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Default Output classes A and AB

Please note the interpolations.

On Oct 24, 3:42 pm, flipper wrote:

This is what I meant. People seem to be losing track of who said and
meant what.


I am not so sure that losing track is the correct description of what
is going on. It more-or-less started with a statement that a Certain
Amp was a Model for various reasons amongst which was an apparent
broad Class A operational range before it went to AB.

So, an amplifier *may* operate in Class A mode for some range based on
its design.


I may have missed something but as far as I can tell *that* is the
'argument'.


I don't think anyone would disagree even for a hummingbird heartbeat
that some AB amps have some range of A operation before they go AB. It
is how one would describe and represent the amp overall that is at
issue.

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.


I haven't seen anyone claim that a Class AB amp is 'actually' a Class
A amp, or should be 'classified' as an 'A' something, or any variation
of the theme.

Otherwise, what we have is a marketing ploy because as previously
stated: Class A = Good Class AB = Not So Good


I think you're worrying about something that no one in here is guilty
of and, near as I can tell, the 'argument' revolves around the claim
by Multi-grid:

"That both tubes are conducting does not mean it is
A. Have some respect... AB amps don't have any A power, that is why
there is a separate classification."


It would seem to me that with your comment above saying "an amplifier
*may* operate in Class A mode for some range" that you are disagreeing
with Multi-grid.


I do not necessarily agree with Douglas. I just find the rebuttals to
his statements mostly either technically inept (as from Andre) or
technically elegant (as from John) but beside the point.

Btw, just as a matter of discussion, I see where you're trying to go
with the V8 analogy but I don't think it holds, as given, because 2,
4, 6, and 8 cylinder operation is not a 'natural' consequence of the
'engine class V8' while 'A' and 'B' (loosely defined) are for 'Class
AB'.


Actually, it was John that postulated a series of controls on an AB
amp that would force it (hold it in) to A class only. So, the analogy
of an 8 held to 4 or 6 cylinders only holds under that description.

I think a closer, albeit still 'stretched' quite a bit, analogy would
be if we defined 'engine classes' 4, 8 and "4-8," and then pondered if
a 'Class 4-8' engine was operating 'Class 4' during the times when
only 4 of the cylinders were firing. If the definition for 'Class 4'
was "4 cylinders firing" then one might say it was, despite some
differences, since 4 cylinders are firing under those conditions; Akin
to 'Class A' being the tubes conducting 360 degrees, a situation that
occurs in Class AB amps under certain conditions.


Oh, the entire engine analogy is stretched more than taffy on a hot
day in Atlantic City. But for all that, it is as valid as any other
points made along the line in this particular thread - again excepting
the direct contributions from Patrick which are right into the nitty-
gritty of the situation.

And one might wish to talk about under what conditions the 'Class 4-8'
engine makes the transition from 'Class 4' to 'Class 8' operation
because if it did so at the slightest hint of needing more power it
might make for 'zippy' performance at the expense of fuel efficiency
while a 'Class 4-8' engine reluctant to do so might be more efficient
at the expense of 'zippy' throttle response. But, IMO, saying "it's
Class 4-8, period, there is no Class 4 power" simply serves to obscure
it's operation for no useful purpose.


Well, it ain't nohow a "4-only" and it ain't nohow an "8-only", so it
must be something else. The only accurate label would be a "4-8". That
it operates in either mode is a function of its design. But it belongs
to neither unique class.

It might also be useful to point out, as you did, that 'Class 4'
operation of a 'Class 4-8' engine is not '100% equivalent' to 'Class
4' operation in a true 'Class 4' engine (depending on how well
designed each is) because you're dragging along dead cylinders, a
necessary consequence of it being a 'Class 4-8' engine, and, by the
same token, 'Class A' operation in a Class AB amp is not '100%
equivalent' to a true Class A amplifier (depending on how well
designed each is) for the same reason: the 'Class A' region of a Class
AB amp is compromised by the necessities of it being a Class AB amp.


Yep. And that is contributory to the point but not critical to it.

However, there's nothing in the 'Class' definitions that speaks to
'optimal', 'well designed', or 'equivalencies'.


Amen to that! There is quite a bit of ineffable crap out there. Some
of it is very expensive and uses very expensive boutique-type tubes
for no other reason than that they are expensive boutique tubes -
certainly not for the quality of the signal coming out of them. Why,
even their makers and defenders will wax poetic about how these amps
"add coloration" to the signal that makes them an "instrument in their
own right" and such twaddle. It is those sorts who will wax poetic
about that little bit of "Class A" operation in an AB-designed amp as
some great virtue. In point of fact, this would necessarily require
that the AB operation of the same amp is somehow faulty. Otherwise a
properly designed amp would be A only and t'h*ll with the headroom.

Once again, unless we are dealing in an Orwellian world, it just isn't
necessarily so.

Peter Wieck
Wyncote, PA



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Default Output classes A and AB

In article . com,
Peter Wieck wrote:

It is those sorts who will wax poetic
about that little bit of "Class A" operation in an AB-designed amp as
some great virtue. In point of fact, this would necessarily require
that the AB operation of the same amp is somehow faulty. Otherwise a
properly designed amp would be A only and t'h*ll with the headroom.


I don't see how the one follows from the other, could you please explain
the logic you used in arriving at this conclusion?


Regards,

John Byrns

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Default GM V8-6-4 (was Output classes A and AB)

In article .com,
Peter Wieck wrote:

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?


I'm not sure it was a pure marketing ploy, especially given that I have
seen ads for a current model car that uses this same idea today,
unfortunately I forget what car it is, it might even be a Cadillac,
although I would think they would be too gun shy to try it again. At
any rate the reason I started this sub thread was to ask if anyone more
knowledgeable about engines than you or I knows the theory of the 8-6-4
engine and how it was supposed to improve gasoline mileage, which as I
remember it was what the hype said it was supposed to do? The only
potential efficiency gain that I can see is that it would presumably
reduce throttling losses a bit, but there must be more to it than just
that, does anyone know? I guess I should ask Google.

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


Better solution for what problem?

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?


Yes, but a 4 cylinder engine with the power of a V8 might be a little
rough for many Cadillac buyers.

And that would, of course, cost a pretty penny - more than a similar
displacement & output V8?


I would expect that a V8 would cost more than a 4 of similar
displacement, simply based on the parts count, but what do I know. The
4 would probably require some more expensive drive train parts than the
V8, at least in manual transmission applications.


Regards,

John Byrns

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Default Output classes A and AB

In article .com,
Multi-grid wrote:

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

Odd sums anyway.


Thanks for that clarification.

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 ).


That's a bunch of nonsense and drivel, if the cancellation were simply
the result of "the finals are biased so that the change in
characteristic for the opposing phases approximately cancels", then the
amount of odd order distortion could also be changed by PP connection.
The fact is that the even order cancellation is not dependent on the
biasing of the tubes, beyond the requirement that the two tubes are
identical and are both biased the same.

Check your High School Trigonometry book to understand why the even
harmonics cancel while the odd ones don't, it's a simple bit of math
that doesn't depend on bias, only that the two sides of the PP circuit
are identical. IIRC even PP class C amplifiers cancel even order
distortion, this was made use of in early FM broadcast transmitters to
minimize interference with high band VHF Television stations, without
the need for a harmonic filter in the output of the FM transmitter.

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 ).


It isn't obvious by what logic you arrived at that conclusion?

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


You aren't by any chance one of Peter Wieck's sock-puppets are you?

AB was an obvious means of minimizing cross-over distortion


Class AB simply moves the crossover notch up to a higher amplitude point
on the signal waveform, if you really want to minimize the crossover
notch you should have Patrick design and wind you an OPT designed
specifically to minimize the crossover notch, or go with a McIntosh
design.

and maximizing power.


Class B operation would be even better for 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...


Yep, it sure is great stuff!


Regards,

John Byrns

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Default Output classes A and AB

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


Well, yes, but who would want a strictly Class B tube amp? It'll be
harsh and nasty and the THD will be grim. On the other hand, there was
an urgent demand (possibly only from the marketing department,
possibly from speaker manufacturers -- these things are very rarely
consumer-led) for more output than available from SE or even Class A
triodes. Class AB, a natural for the new multi-grid tubes, was for the
time a perfect compromise between the "waste" of Class A and the (at
the time) incredible power available from push-pull operation of beam
tubes and pentodes, *and* Class AB had a lower NFB requirement than
Class B, all others things being equal of course, and thus better
stability margins. All of this happened at the same time ever-lower
THD numbers became the chief marketing tool; it followed in turn that
the THD should be attacked where it was most vulnerable and where it
would give the biggest fix in the least time for the lowest cost, and
that was at the second harmonic. So, you don't want Class B because it
is crude, you can't have Class A because it is too expensive for the
power you want, you must have a lot of stable power with low THD,
bingo, Class AB saves your butt. You have to look at the entire
package of elements that drove the general swing towards Class AB.

Having looked, from a closer vantage point than ours, at the package
of elements, Langford-Smith himself tells us in the RDH4 (Newnes
1997) on p 545 that:
"Class AB operation indicates overbiased conditions, and is used only
in push-pull to balance out the even harmonics."

In Langford-Smith's eyes, therefore, it seems that what drove the
choice of Class AB was the ability to retain most of the power
available in Class B while reducing THD a very big chunk, without the
instability that would follow on the heels of the amount of NFB to
achieve the same task in Class B.

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.


Sure, Class A1 amplifiers, as in SE 300B amps, are big since say the
mid-80s. But I think if you go into the history of how much of the
total power of typical Class AB amps at every period was available in
Class A, I think you will find that in the days of sensitive speakers,
when the first watt truly was everything that mattered, the Class A
benefice was quite low, a handful of watts perhaps. It is only in fact
since the 1950s that it was known to specialists that third and higher
odd harmonics are disproportionately more disturbing than the even
harmonics; you can still see the willful resistance, arising from
ignorance, to my practice of designing amps to shape the residual
harmonic artifacts so that the odd residuals are miles below the
fractional remaining second harmonic. Again, those tubes like 807s
when operated in triode were naturals for Class AB, with a naturally
beneficial harmonic spectrum; these things fell out naturally without
the obsessive thought we put into the tiniest detail these days,
bedevilling retrospective analysis.

Regards,

John Byrns

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


Of course I could be wrong. I wasn't there, I don't have twenty-twenty
hindsight, and the few amps whose histories I know about are not
exactly in the mainstream. One has to read very carefully between the
lines to understand what someone like Langford-Smith tell you when he
speaks of motives driving commercial choices rather mere engineering
facts: his milieu and assumptions were very far from ours.

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

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Default Output classes A and AB

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.


I've already demonstrated several times that your words "under
any signal condition" make your definition grossly inaccurate. I have
already told you, Poopie Stevenson, three times that your definition
is grossly inaccurate and why. Worse, you, Poopie Stevenson, have
already admitted that your definition should be rewritten as I told
you to rewrite it, three times in all:
******
Poopie wrote:
Do please, if you desire, change it to 'any valid signal
condition for which the amplifer is rated'.

******
Nah, Poopie, we don't only desire it, we demand it, because this kind
of ignorance that you display so stubbornly reflects badly on all of
us.

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.


Precisely. That is what I explained to you, three times in all, plus
once more from Flipper, before you finally understood and stopped
following along behind Dougles Zero-sound like a fat little lost lamb.
You are a very slow learner, Poopie.

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


Me? Come on, Poopie, I'm not the one who claimed for several days that
a Class A stage is one in which "the output device(s)never cease
conducting *under any signal condition*." You're the one who committed
that stupidity, and so many others. *You* really should constrain
yourself to talking about stuff you understand -- which would seem not
to be very much going by your posting history.

Graham


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



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Default Output classes A and AB

Poopie Stevenson aka Eeyore
wrote:
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.


Now this poor dumb slow learner Poopie Stevenson, an embarrassment to
everyone who comes into contact with him, claims to know more than the
RDH4! Yo, Poopie, in the RDH4 (Newnes 1997) on p 545 we find this
nugget of authoritative information by F. Langford-Smith B.Sc. B.E.
himself:

"Class AB operation indicates overbiased conditions, and is used only
in push-pull to balance out the even harmonics."

You're a fool, Poopie. You should have taken a tip from John Byrns and
asked a question rather than made a statement you cannot back up.

The dissipation in the output tubes is very considerably lower than that in
Class A.


You're blowing smoke out of your arse, Poopie. I'm clearly talking
about output power but you try to muddy the water with "dissipation in
the output tubes". You're not only a clown, you're a transparent
clown.

Or are you perhaps, in line with the ignorance generally displayed in
your posting history, trying to claim that more output power is
available from Class A than from Class AB? That would be a new nadir
of stupidity even for a man who just claimed that Class A devices
should conduct 360 degrees "under any signal condition".

Graham


Andre Jute
The trouble with Poopie Stevenson is not what he doesn't know, but
what he knows for certain that isn't true. --- with apologies to Mark
Twain


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Default Output classes A and AB



That's a bunch of nonsense and drivel, if the cancellation were simply
the result of "the finals are biased so that the change in
characteristic for the opposing phases approximately cancels", then the
amount of odd order distortion could also be changed by PP connection.
The fact is that the even order cancellation is not dependent on the
biasing of the tubes, beyond the requirement that the two tubes are
identical and are both biased the same.


So then John, when one is cut off, what is cancelling?

and on this: "The fact is that the even order cancellation is not
dependent on the biasing of the tubes, beyond the requirement that
the two tubes are identical and are both biased the same.

And how are two tubes 'the same' when one is in the traditional AB
bias piont? Further, as one starts cutting off( not far from its idle
point ), how is this remotely like what is going on in the other
phase?

I'll give you a hint.....nah, you'll get it eventually.

Do try and keep your answer out of the Nonsense&Drivel category.
cheers,
Douglas







Check your High School Trigonometry book to understand why the even
harmonics cancel while the odd ones don't, it's a simple bit of math
that doesn't depend on bias, only that the two sides of the PP circuit
are identical.


No kidding. Where would one get these magical identical tubes?

Getting a class A amp to cancel its 2nd HD is not a trivial exercise.
I suggest you try it on your AB amps, just for kicks.
cheers,
Douglas


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Default GM V8-6-4 (was Output classes A and AB)

At
any rate the reason I started this sub thread was to ask if anyone more
knowledgeable about engines than you or I knows the theory of the 8-6-4
engine and how it was supposed to improve gasoline mileage, which as I
remember it was what the hype said it was supposed to do?


Internal combustion efficiency is determined by the compression ratio.
High-vacuum conditions reduce the effective compression ratio. Going
to smaller displacement( through de-activating cylinders) meant
operation at higher manifold pressure, and thus higher
compression( from a given cam timing and combustion chamber geometry).

Unfortunately, you were dragging along other cylinders. There were a
few means of reducing the pumping losses, some worked better than
others. Also, the inactive cylinders were rotated in order to maintain
operating temperatures.

There's more to it, but those are the broad strokes.
cheers,
Douglas

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Default Output classes A and AB

In article .com,
Multi-grid wrote:

That's a bunch of nonsense and drivel, if the cancellation were simply
the result of "the finals are biased so that the change in
characteristic for the opposing phases approximately cancels", then the
amount of odd order distortion could also be changed by PP connection.
The fact is that the even order cancellation is not dependent on the
biasing of the tubes, beyond the requirement that the two tubes are
identical and are both biased the same.


So then John, when one is cut off, what is cancelling?


The even order spectral components of the distortion products produced
in each of the two tubes, including cutoff effects.

and on this: "The fact is that the even order cancellation is not
dependent on the biasing of the tubes, beyond the requirement that
the two tubes are identical and are both biased the same.

And how are two tubes 'the same' when one is in the traditional AB
bias piont?


Both tubes must be at the same bias point, be it "traditional AB" or
whatever other bias point floats your boat.

Further, as one starts cutting off( not far from its idle
point ), how is this remotely like what is going on in the other
phase?


Because both tubes are doing exactly the same thing over a complete
cycle, except out of phase.

I'll give you a hint.....nah, you'll get it eventually.


No, I don't think I will ever get "it" unless you give me a hint.

Do try and keep your answer out of the Nonsense&Drivel category.


Done.

Check your High School Trigonometry book to understand why the even
harmonics cancel while the odd ones don't, it's a simple bit of math
that doesn't depend on bias, only that the two sides of the PP circuit
are identical.


No kidding. Where would one get these magical identical tubes?


To the extent that you can't get magical identical tubes you will have
to settle for less than complete even order distortion cancellation.

Getting a class A amp to cancel its 2nd HD is not a trivial exercise.


It's easy enough, trivial even, to adjust the differential bias so a
single even order harmonic is canceled, even with non-identical tubes.

I suggest you try it on your AB amps, just for kicks.


My amp operates class A.

Are you saying that getting a class A amp to cancel its 2nd HD is more
difficult than getting a class AB amp to cancel its 2nd HD, or vice
versa, or neither?


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/
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Default Output classes A and AB



Andre Jute 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.


I've already demonstrated several times that your words "under
any signal condition" make your definition grossly inaccurate.


But you're an ignorant **** and what you say is a load of ********.

"In a Class A circuit, the amplifying element is biased so the device is always
conducting to some extent"
http://en.wikipedia.org/wiki/Electro...lifier#Class_A

You're confusing cause and effect but your brain is too addled to understand the
difference.

Graham



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Default Output classes A and AB



Andre Jute wrote:

Eeyore wrote:

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


Me? Come on, Poopie, I'm not the one who claimed for several days that
a Class A stage is one in which "the output device(s)never cease
conducting *under any signal condition*." You're the one who committed
that stupidity, and so many others.


And * so many others* too eh ? Ever consided we might actually be right ?

You're a ****ING CRETIN Joot. Go back to the miserable hole you crawled out of.

Graham

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Default Output classes A and AB



Andre Jute wrote:

Poopie Stevenson aka Eeyore
wrote:
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.


Now this poor dumb slow learner Poopie Stevenson, an embarrassment to
everyone who comes into contact with him, claims to know more than the
RDH4! Yo, Poopie, in the RDH4 (Newnes 1997) on p 545 we find this
nugget of authoritative information by F. Langford-Smith B.Sc. B.E.
himself:

"Class AB operation indicates overbiased conditions, and is used only
in push-pull to balance out the even harmonics."


It's the push-pull that cancels those harmonics YOU UTTER CRETIN ! A Class **A**
push-pull output stage will do that too.

AB operation has NOTHING to do with distortion cancellation.

Your problem is that you don't understand what you'r reading so you quote out of
context as a result of your utter IGNORANCE.

Graham
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Default Output classes A and AB

On Thu, 25 Oct 2007 10:26:32 +0100, Eeyore
wrote:



Andre Jute wrote:

Poopie Stevenson aka Eeyore
wrote:
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.


Now this poor dumb slow learner Poopie Stevenson, an embarrassment to
everyone who comes into contact with him, claims to know more than the
RDH4! Yo, Poopie, in the RDH4 (Newnes 1997) on p 545 we find this
nugget of authoritative information by F. Langford-Smith B.Sc. B.E.
himself:

"Class AB operation indicates overbiased conditions, and is used only
in push-pull to balance out the even harmonics."


It's the push-pull that cancels those harmonics YOU UTTER CRETIN ! A Class **A**
push-pull output stage will do that too.

AB operation has NOTHING to do with distortion cancellation.

Your problem is that you don't understand what you'r reading so you quote out of
context as a result of your utter IGNORANCE.

Graham


Graham, please just killfile the idiot like most of us have. His
dribbling meanderings are just as irritating at second hand as they
are when they have dropped fresh from his rear end.

d

--
Pearce Consulting
http://www.pearce.uk.com
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Default GM V8-6-4 (was Output classes A and AB)


"John Byrns" wrote in message
...
In article .com,
Peter Wieck wrote:


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?


If not a rhetorical question, then this is a straw man argument, as the
relevant products are still called V-8s by the marketing people.

I'm not sure it was a pure marketing ploy, especially given that I have
seen ads for a current model car that uses this same idea today,
unfortunately I forget what car it is, it might even be a Cadillac,
although I would think they would be too gun shy to try it again.


AFAIK, the technology is being used in current production GM and Chrysler
cars. I have friends who drive them.

At
any rate the reason I started this sub thread was to ask if anyone more
knowledgeable about engines than you or I knows the theory of the 8-6-4
engine and how it was supposed to improve gasoline mileage, which as I
remember it was what the hype said it was supposed to do?


A cylinder in a gas engine uses more energy if it is only partially in use
than if it is turned off. Some losses stay about the same, but other losses
are vastly reduced if you partially turn the cylinder off by means of
significantly altering the valve timing. AFAIK, the spark plug still fires
but no fuel is injected, and the amount of air that the cylinder pumps is
vastly reduced.

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


Better solution for what problem?


Better than operating with a very tightly closed throttle. The engines that
receive this treatment are relatively large and powerful. They are
agressively throttled back most of the time.

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?


Approximately yes. Engines are built with as many cylinders as possible to
smooth the noise and vibration. They are built with as few cylinders as
possible to reduce production costs. But, varying the number of cylinders
has secondary effects, such as the torque curve, etc.

Yes, but a 4 cylinder engine with the power of a V8 might be a little
rough for many Cadillac buyers.


Cars with very large 4 cylinder engines have been built. One was built on
half of a V8. It was rough and noisy, not to mention being on the heavy
side. These days most larger in-line 4 cylinder engines have a balance
shaft to cancel out some of the secondary shaking motions.

And that would, of course, cost a pretty penny - more than a similar
displacement & output V8?


A really big 4 would be cheaper to build, all other things being equal.

I would expect that a V8 would cost more than a 4 of similar
displacement, simply based on the parts count, but what do I know.


You would be right.

The 4 would probably require some more expensive drive train parts than
the
V8, at least in manual transmission applications.


I don't know about that. For one thing, we haven't said which configuration
4 this is. IME flat 4s put out a lot of low end torque for their
displacment, and require beefed-up drive trains that can handle it. In-line
4s and V6s and V8s seem to be lower on low end torque for a given
displacement and stroke/bore, and can probably get by with less beef in the
clutch, tranny, differential, and CV joints.


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Default Output classes A and AB


"Eeyore" wrote in message
...


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.


Agreed.

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.


Agreed. Jute seems to be addicted to excluded-middle arguments. Kick out
those and the straw men, and he's hardly have anything to say. ;-)

You really should constrain yourself to talkind about stuff you
understand.


It would save a lot of bandwidth.

Which would seem not to be very much going by your posting history.


Jute is mostly about hyperbole. In real life he makes Walter Mitty look
like a world-class adventurer. ;-)




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Default GM V8-6-4 (was Output classes A and AB)

On Thu, 25 Oct 2007 05:56:37 -0400, "Arny Krueger"
wrote:

A cylinder in a gas engine uses more energy if it is only partially in use
than if it is turned off. Some losses stay about the same, but other losses
are vastly reduced if you partially turn the cylinder off by means of
significantly altering the valve timing. AFAIK, the spark plug still fires
but no fuel is injected, and the amount of air that the cylinder pumps is
vastly reduced.


In the huge diesels that routinely turn off multiple cylinders, the
valve gear is uncoupled so the valves remain closed. That way no air
is pumped and the losses drop to negligible levels. You really don't
want to be shifting air, even if there is no combustion, if economy is
your objective.

d

--
Pearce Consulting
http://www.pearce.uk.com
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Default Output classes A and AB

On Thu, 25 Oct 2007 06:00:25 -0400, "Arny Krueger"
wrote:


"Eeyore" wrote in message
...


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.


Agreed.

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.


Agreed. Jute seems to be addicted to excluded-middle arguments. Kick out
those and the straw men, and he's hardly have anything to say. ;-)

Can you overdrive a class A amp to cutoff? In my experience what
happens when you overdrive a class A amp is that one device saturates,
and the other sticks with its normal bias condition. There is no
circumstance in which I have ever managed to put a class A amplifier
output device into cutoff.

d
--
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http://www.pearce.uk.com
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Default Output classes A and AB


"Don Pearce" wrote in message
...
On Thu, 25 Oct 2007 10:26:32 +0100, Eeyore
wrote:



Andre Jute wrote:

Poopie Stevenson aka Eeyore
wrote:
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.


Or bits of silicon, or whatever amplification device is being used.

Now this poor dumb slow learner Poopie Stevenson, an embarrassment to
everyone who comes into contact with him, claims to know more than the
RDH4! Yo, Poopie, in the RDH4 (Newnes 1997) on p 545 we find this
nugget of authoritative information by F. Langford-Smith B.Sc. B.E.
himself:


"Class AB operation indicates overbiased conditions, and is used only
in push-pull to balance out the even harmonics."


No such thing in the RDH4 at hand.

It's the push-pull that cancels those harmonics YOU UTTER CRETIN ! A Class
**A**
push-pull output stage will do that too.


Agreed.

AB operation has NOTHING to do with distortion cancellation.


Agreed.

Your problem is that you don't understand what you'r reading so you quote
out of
context as a result of your utter IGNORANCE.


Seems like Jute has his own private translation of the RDH4 that adds errors
to what the original authors wrote.

Graham, please just killfile the idiot like most of us have. His
dribbling meanderings are just as irritating at second hand as they
are when they have dropped fresh from his rear end.


The guy who manipulates the Jute sockpuppet is an attention-hound, pure and
simple.


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Default GM V8-6-4 (was Output classes A and AB)


"Don Pearce" wrote in message
...
On Thu, 25 Oct 2007 05:56:37 -0400, "Arny Krueger"
wrote:

A cylinder in a gas engine uses more energy if it is only partially in use
than if it is turned off. Some losses stay about the same, but other
losses
are vastly reduced if you partially turn the cylinder off by means of
significantly altering the valve timing. AFAIK, the spark plug still fires
but no fuel is injected, and the amount of air that the cylinder pumps is
vastly reduced.


In the huge diesels that routinely turn off multiple cylinders, the
valve gear is uncoupled so the valves remain closed.


Thats about the same as what they do in the cars I mentioned.

That way no air
is pumped and the losses drop to negligible levels.


Agreed.

You really don't
want to be shifting air, even if there is no combustion, if economy is
your objective.


That seems to be how the technology works. I am informed by my friends who
have cars that implement this strategy, that there are consistent and
significant real-world fuel economy gains, as measured by modern car
computers that display dynamic fuel economy measures.


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Default Output classes A and AB



Andre Jute wrote:

On Oct 24, 6:57 am, flipper wrote:
On Wed, 24 Oct 2007 13:44:13 +0100, Eeyore



wrote:

Patrick Turner wrote:


Eeyore wrote:
Multi-grid wrote:
maxhifi wrote:


Stating that "the amplifier is Class A until XXX watts", really, is
telling you how hot the tubes are biased relative to the two extremes of
pure class A (full dissapation), and pure class (cut off).- Hide quoted text -


Class A has nothing to do with dissipation either. Just because some
marketing group noticed that class A means something good, does not
make it right either. Just because it seems to make sense is no reason
to *******ize the definition. Find some other way to describe it.


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.


People are talking semantically past each other with some speaking of
the definition of the 'amplifier' class while others are speaking of
it's behavior under a restricted set of operating conditions; and it
is useful to observe that under an appropriately restricted set of
conditions the output tubes conduct 360 degrees as in 'Class A'
operation.


"Useful", indeed, Flipper. Thanks. But I would go further and say that
the signal and dissipation restriction is part of the definition, as
you go on to imply:

For example, if maximum power, or efficiency, were the primary concern
then one might bias more to the 'B' side of the equation while if
fidelity were the primary concern one might bias more to the 'A'.


Precisely. Both Class A operation and Class B operation are inherent
in the nomenclature and definition and their relative importance is
clearly intended to be in the designer's discretion.

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. 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.


He he, No, The largish % of class A power in an "AB" amp is a very very
rare trend these days.

I cannot think of a single PP amp which has a large % of class A power.

ARC and CJ and most others are locked into a stupid desperate war of
watts, where they
try to extract a maxima of class AB watts and to hell with class A, and
reliability.

Who is going to buy a class AB amp with 2 x 6550 per channel that puts
out a "parsimonious 50 watts"
when the guy down the road is making a similar amp which puts out 75
watts?
Hell, may as well try for 100 watts.

The Chinese meanwhile are dumping absolute crap onto the market which
falls apart or burns out sooner rather than later
and distracts buyers from spending on ARC and CJ who of course have
prices which are 15dB higher than the Chinese amps.
To try to snare sales though, the big US brands try to extract more
power, its like they
can't bare to be seen to make 40 watt amps with a pair of 6550 and then
be seen to charge the 15dB more.

What the big makers do, ARC, CJ and many others around the globe is just
raise the B+, and lower idle current,
and then lower the RLa-a and presto, you have a raw PA amp around which
you run about
12dB max of GNFB, and call it hi-fi, but your lucky if there is 5 watts
of class A before the amp lurches into
class AB for the majority of the power ability of 75 watts which BTW
will NEVER get used.

Amp manufacture has, like 1,001 other products become a marketting
exercize,
not any thing else. Certianly not an exercize in providing maximal
fidelity
with a minimum of NFB.





One might also observe that's likely why it's called Class AB and not
Class insert unique letter.


There is in fact a class between Class A and Class AB with a unique
description: "Limiting Class A1", which is set up so that the
crossover happens when one valve just reaches current cutoff and the
other simultaneously reaches zero bias. It makes for an amazingly
smooth sound but it is a bitch to set up and keep tuned if you want to
keep your circuits simple. I was therefore rather interested in what
Patrick said elsewhere in this thread (in more general sense rather
than specifically about LImitiing Class A1) about within 10 per cent
of conduction angle being imperceptible...


Limited class A is the correct term, not limiting, which can mean
something else.

All PP class AB amps are capable of producing class A power only and
never moving into class AB.

And I meant what I said about defining the class A. Class A in a PP amp
is where the anode current is *always* at leasst above 10% of the idle
current.
So where you have 50mA of idle current in each of the PP tubes, and an
Ia swing of +/- 45mA,
each tube is working in PURE class A, and thus the pair are ALSO said to
be working in pure class A.

Suppose you have a pair of tubes, fixed bias, B+ = +500V, and a swing of
+/- 350Vpk
on each tube. There is 700Vpk a-a, = 500Vrms.
Let us say the Ia change at each anode = + or - 45mApk, then the RL seen
at each anode
while working in pure class A = 350V / 0.045A = 7.78k.

Effectively, the OPT places these loads in series, and you have a load
RL a-a = 2 x 7.78k, or 15.6k.

With 500vrms across 15.6k, you get 16 watts of pure class A.

The idle pda for each tube = 500V x 0.05A = 25 watts, so for 2 tubes its
50 watts.
Efficiency maximum = 16 / 50 = 32%.

We would be describing approximately the outcome with a pair of pure
class A KT88 in triode.

So what happens when we use a 5k load on the same amp?

The same idle current flows, and the same range of Ia variation 0f +/-
45mA will define the
class A **current** swing, ( where the **current** wave THD 5% and
mainly all 2H ).

So the class A load on each tube = 1/2 x 5k = 2.5k, so the maximum class
A V swing at each anode
= 2,500ohms x 0.045A pk = 112.5Vpk = 225pk from anode to anode, or
159vrms across 5k,
giving 5 watts of class A.

But the load value allows for a much larger increase in Ia than the 50mA
of maximum decrease in Ia.

This also means that once the Ia travels below 10% of the idle value,
the gm of the tube cutting off
has diminished to such a low value the other tube turning on harder is
providing virtually all the Ichange x Vchange
across the available load, and is the only device coupled through only
1/2 the OPT primary
to the load, so the RL seen by this tube turning on hard has reduced to
1/2 its class A load,
or 1/4 of the nominal RL a-a, and in this case its 1.25k.

The load is the same as that for a class B amp.

Load lines will describe it all far better at my website. But you would
find that triodes
in AB with Ea = 500V, and load of 5ka-a can make a peak Emin = 220V, so
swing = 500-220 = 280V,
and at this point peak Ia = 220mA approx on each output tube, and this
operation is at the limit
of operation without being hindered by grid current.
So pk a-a sw = 560V pk = 396vrms, and this means you get 31 watts of
class AB power into 5k.

5 watts of pure class A is possible, then the operation ***gradually***
changes from
impure class A to AB, where one tube cuts off gradually, and the other
tube turning on reaches
a peak current several times the idle value.
if the current waves in each tube are examined, with a 5k load the waves
are seen to have about 5%
mainly 2H when making 5 watts into 5k, but at 31 watts, the current THD
becomes
over 20% with lots of harmonics.
Most don't reach our ears because of the complementary action of the two
tubes.

Pentodes and beam tetrode amps have less gradual change than triodes
when passing from class A to class AB,
and in fact generate far more dirty sounding "switching" harmonics
higher than 2&3H in what is called the "switching zone"
or "crossover region".
McIntosh became renowned for producing 50 watts from a pair of 6L6
running
them in low bias current class AB, and applying a total huge amount of
local and global
NFB to get the Rout and THD/IMD low.
ARC use 16 x 6550 in their reference 600 amps to make 600 watts.
This means there is 75 watts coming from each pair of PP output 6550.

Not much class A power though.

I have just completely re-engineered and re-wired an ARC VT100, made in
1996.
It has 4 x 6550 per channel.
I found that when there was 8 ohms connected to the 0-8 outlet,
you'd get about 125watts of AB power, but very little class A because
the tubes were being pushed hard into class AB1.
8 ohms was the load where maximum PO is available.
I found that using an 8 ohm load connected to the 0-4ohm outlet
gave less maximum PO, about 75 watts but a much higher % of class A po
before class AB PO begins.

The speakers I have to test this amp for any remaining bugs have 8 ohm
woofers for 20Hz to 250Hz,
and a pair of 6 ohm SEAS midranges in series for 250Hz to 3.2kHz and a
dome 6 ohm SEAS tweeter
for above 3.2kHz.
The speaker Z is thus well above 8 ohms in the main power band for
music,
and when cranked loud, the amp's new green-red LEDs which indicate Idc
at the cathodes do not
change from the correct pale green to red.
There is plenty of class A power AND GREAT NATURAL FIDELITY available.
Some folks would insist in using "4" ohm speakers with dips in the main
power band to 2 ohms,
and connect to the 0-4 ohm outlet **which really should be labelled
0-8**.
The 0-8 outlet should be re-laelled 0-16 ohms.

The use of speakers with Z = average 3 ohms instead of 10 ohms like I
have means
that the THD/IMD will be approximately 3 times as high for the same PO
as with 10ohms, class A power is reduced to near nothing,
and the damping factor is hopeless.
Class AB PP amps have a varying Rout which is lowest while
the amp works in class A, but which doubles when in class AB at extremes
of wave points. This unfixed Rout translates to compression,
massive 3H, and lots more IMD than while working in class A.

Anyway, the quad of 6550 while working in class A with a 10ohm load
connected
across the mis-labelled 0-4 ohm outlet do sound VERY well.

Those wanting a schematic of what have done may ask as I have a .gif
available.

Its much simpler than the original, and I won't beak ARC rules by
handing out free copies of their
abominable concoctious junk.

The reformed ARC VT100 can make 23Vrms into 8 ohms at its 0-4 ohm
outlet, = 66 watts,
or about 24Vrms into 10 ohms = 57 watts, which is completely plenty!

The 0-8 ohm outlet should ***never be used*** unless you have genuine
16+ ohm speakers,
or perhaps ESL where the Z is high below 1kHhz down to 100Hz, and you
simply need a large voltage drive.
One may always have a high Z midrange ESL across the 0-8 ohm outlet, and
a lowZ woofer
across the 0-4 ohm outlet.

The other config available is the 4-8 connection.
This amount of never-spoken-about-section-of-winding
is equal to 0.293 x the whole secondary winding turns, which is a
theoretical match for 16 ohms, but should have been for 32 ohms.
The 4-8 connection gives a match to 1.37 ohms, if we considered the two
labelled
4 and 8 as right.
In fact, the VT100 would give superlative fidelity into 2.7 ohms
if a speaker of 2.7+ ohms was connected between the 8 and 4 output
posts.

I have set up the VT100 so it has separate bias adjust pots for each
tube,
and Ia+Ig2 at idle = 39mA measured at the cathode. VT100 is a UL amp
with OPT with ct speaker secondary which is optimistically a match for
16 ohms,
and each end applies some local CFB to the output tubes.
I have Ea at +430V, so Pd at idle for each 6550 = 17 watts only.
One can only barely keep a hand on the mesh cover over the tubes even
with such a low Pd at idle.
I sure don't need to run the 6550 any hotter than they are now.
The amp may be played very loud, and music does not unbias the amp
badly.
The total Pd = 67 watts, and if UL class A efficiency max = 45%,
then maximum possible class A from this amp = 30 watts, AND THIS IS
PLENTY!!!

I have also fixed an ARC Reference One preamp to use with the VT100.
One of its EI-6922 had gone noisy.
Its complicated circuit has been left alone except for lifting the OV
rail from the case
and re-connecting via 22 ohms.

The VT100 had a true horror for a PSU and after fitting a CLC B+ filter
and re-locating
earth paths, I finally got hum&noises to be less than 1mV with preamp
gain at max with
open cd input. The ARC Reference one preamp is a fully balanced design
except that the balanced output
isn't from a floating secondary of a transformer. It should be, but
ain't.
Gain max is 12dB, and because there are 8 x 1/2 6922 triodes used in
each channel, with an easily possible open loop
gain of 1,000 at least, I would suppose that the level of global NFB
used around
the totally balanced LTP type stages amounts to about
40dB at least.
Its bandwidth = 1Hz to 680kHz, and noise is low, and it is a superbly
measuring preamp.
But I would get similar sound using 2 triodes instead of 8 in a line
stage, and have no need for balanced at all.
The ARC preamp does seem to be sonically neutral as one would expect
from a totally pure class A amp with a shirtload and bootful of NFB.
I am amused at those who would say that changeing from say Sovtek
6DJ8/6922
will change the sound from say Siemans NOS 6DJ8. I would always suggest
that the high amount of NFB
must blind the listener to sonic variations, since any artifact or sonic
signature is cancelled away by the NFB action.


For a lot more about class A and AB in power amps, go to the
educational/diy pages at my website.
http://www.turneraudio.com.au

Patrick Turner.














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



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John Byrns wrote:

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?



Class AB was found to be more efficient and cheaper per watt to produce,
and give better sonic performance than the SE amps of 1935.
Once anyone needed more than 3 watts, PP was considered,
and the bonus was to banish high THD/IMD of the SE amps of the day.
The SE radio amps using a lone 6V6 in beam tetrode mode with no NFB were
often used,
and had mainly 2H, but many OTHER H, and sounded lousy over a whisperish
level.

HOWEVER, in the misplaced zeal to banish 2H and settle for the clean PP
sound, especially
when you had a pair of output 2A3, designers would labour away to force
an input triode to feed and IST to
drive the PP outputs with a two phase secondary.
SUN amps are a classic example.
Typical primary voltage needed at the 1:2 IST = 50Vrms.
So the bloomin input driver tube was making lots of 2H and there was NO
net betterment in the sonics except
that because the power ceiling was slightly higher.

More thoughtful PP amps were designed in the late 40s by leak, Quad,
Radford etc, where
ALL distortion was considered bad, and where the driver stages were
designed to produce far less THD/IMD
than the output stage.
The Williamson is a classic example.
It can be used with 300B in the output, and NFB needn't be used, and
THD/IMD will remain low enough,
and the 28 watts AB1 will be enough for most folks even now with
insensitive speakers.
With sensitive speakers of the 50s, the 28 watts of AB triode power
was the equivalent of having 112 watts today on average.

But very very fine SE amps can be built, and the 2H is low,
along with other H, and not much NFB need be used.

Patrick Turner.



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/

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Multi-grid wrote:

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*.


Cancelation of even order harmonics occurs in amps working in class AB
during that part of the wave forms which are in class A, ie, the bits
either side
of the zero crossing.

But once each tube moves into cut off, nothing is cancelled.
The two non linear current waves in the tubes of the AB pair
are summed, and the VOLTAGE total is substantially linear, with a small
fraction of the
THD of each tube's current wave.

Its magic, but it works for most ppl.



Odd sums anyway.


Depends on the phase of the harmonics relative to fundemental.

Its possble to have the 3H of the driver stage acting like compression,
and the 3H of the low bias current output stage with 3H acting like
expansion,
and then there is the transformer 3H etc.....

Nothing is general, generic, or simply explained for all occasions, he,
he.


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 ).


Ah, but all AB amps start off with at least a bit of pure class A before
beginning to work in AB.

Even transistor amps with miniscule bias currents, and acting very close
to pure class B amps.
There is always some little bit of class A power where the I swing +/-
is less than the idle current.
That's class A.

Its not the most wonderful class A, but its still 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.



Indeed it was, and still is.


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


Purists don't like impurity like the Pope don't read Penthouse.

Class AB triodes are NOT much used because the 3H is considerable,
and for a given % of 3H, its 9/4 times worse than the same % of 2H.
Some say its 27/8 times worse.

But its never the THD itself that bothers, because music is mainly all
harmonic which are related
except for some notes which ain't related and the transients; drum beats
etcs.

Its the resulting IMD that really grates, and the sum and difference
frequencies produced
when a zillion F are in the amp at the same time dynamically adds up to
unwanted grunge
as background noise better abandoned if possible, except abandoning 2H,
3H etc
is not so easy as dropping off an unwanted child at the orphanage.

You gotta cancel it out, not so easy, or feedback it, or prevent it
happening in the first place by using all class A to cover the whole
dynamic range.
So many purists will go for an SE triode operating right in the middle
of its most linear
curve, then use only a small part of the curve, which is nearly
straight,
so the music sounds fine. Horns and SET were made for each other.

I would say that the IMD products produced by an amp with low 2H is
probably
nowhere near as objectionable than the same amount of IMD products
made by a PP amp.
A PP amp which is into AB transition during average levels isn't any
better sounding than the SET...

Patrick Turner.
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Multi-grid wrote:


That's a bunch of nonsense and drivel, if the cancellation were simply
the result of "the finals are biased so that the change in
characteristic for the opposing phases approximately cancels", then the
amount of odd order distortion could also be changed by PP connection.
The fact is that the even order cancellation is not dependent on the
biasing of the tubes, beyond the requirement that the two tubes are
identical and are both biased the same.


So then John, when one is cut off, what is cancelling?


Look at the current wave in each tube. In AB or B the current wave has
SEVERE distortion spectra.
But the voltage across the WHOLE PP OPT primary is largely free of the
horrendous THD in each tubes current wave.

So its THD reduction by complementary action.

Its like two men sawing a log with a long bush saw, with one man at each
end either pulling or pushing the saw
all the way on each stroke. This is class A, and the differences in
applied forces by each man tend to cancel
and a linear saw action results.

In class AB, each man pulls the saw about 1/2 way across the stroke then
lets go,
and the other guy grabs his saw handle and pulls the saw back the other
way.
Each man only mainly pulls the saw in turn, and applied force is jerky,
and frankly,
a difficult way to work; the Union will be down soon to have a go at the
boss who told
the men to saw the log that way.

But in electronics, we can switch things on and off with absolute ease,
and there is no
Triode Union to make a boss's life a misery.



and on this: "The fact is that the even order cancellation is not
dependent on the biasing of the tubes, beyond the requirement that
the two tubes are identical and are both biased the same.

And how are two tubes 'the same' when one is in the traditional AB
bias piont? Further, as one starts cutting off( not far from its idle
point ), how is this remotely like what is going on in the other
phase?

I'll give you a hint.....nah, you'll get it eventually.

Do try and keep your answer out of the Nonsense&Drivel category.
cheers,
Douglas


We all get it in the end....

Check your High School Trigonometry book to understand why the even
harmonics cancel while the odd ones don't, it's a simple bit of math
that doesn't depend on bias, only that the two sides of the PP circuit
are identical.


No kidding. Where would one get these magical identical tubes?

Getting a class A amp to cancel its 2nd HD is not a trivial exercise.


It mainly IS a trivial exercize and was invented about 2 days after the
first triode was made.

Any two tubes are never identical, but are often within 90% equal to
each other.

Therfore the 2H cancelation in pure class A PP is so substantial that
90%
of the 2H of either tube is cancelled away leaving far far less than if
the two tubes were
used in SE & parallel for the same class A power.


I suggest you try it on your AB amps, just for kicks.
cheers,
Douglas


Trying to make the driver stage make distortions that will cancel the
output stage's PP distortions
is extremely difficult to achieve, and nobody sets out to do it. I tried
it, I failed.
Trouble is that PP output tube distortions change in amplitude and
perhaps phase and spectra
with the dynamic changes in loads connected. Speakers are not lile a
simple one value resistance.
One can manage to more easily exploit 2H cancelling phenomena in SE amps
between SE driver and SE output tube.
PP amp makers all sensibly try to make the driver linear, and output
stage linear,
and then not have to apply too much NFB to cancel the little amount of
mainly 3H distortion..

Some think this is BS, and build a class B thing with lots of THD/IMD
without any NFB.
Then they apply lots more NFB than the fella using mainly all class A in
his output stage.
The unruly class B amp with a shirtload of NFB in the output stage
McIntosh, emitter follower etc,
and a bootfull of global NFB has become the natural choice of
profit hungry amp makers. If you hunger for best music, you must spend
more
for the inefficiency costs of class A.

The staus quo among all amps is 95% AB with rough working AB / near B
devices switching with lots of NFB.
5% are either mainly class A, or AB tube amps, or the new PWM amps with
whatever correction facilities thay can muster.
In 20 years time, all the SS AB amps will have become extinct like
dinosaurs.
The PWM amps can sound as good as generic low bias SS amps and be far
more efficient and far cheaper and lighter/smaller.
Tubes will remain if the Greenhouse Police are not too zealous, and they
will hold sway amoung a
small minority of listeners actually willing to put their money on the
sound,
rather like there will always be someone who likes sailing yachts around
the bay,
rather than drive around the bay in a stink boat.

Patrick Turner.
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Eeyore wrote:

Andre Jute wrote:

Poopie Stevenson aka Eeyore
wrote:
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.


Now this poor dumb slow learner Poopie Stevenson, an embarrassment to
everyone who comes into contact with him, claims to know more than the
RDH4! Yo, Poopie, in the RDH4 (Newnes 1997) on p 545 we find this
nugget of authoritative information by F. Langford-Smith B.Sc. B.E.
himself:

"Class AB operation indicates overbiased conditions, and is used only
in push-pull to balance out the even harmonics."


It's the push-pull that cancels those harmonics YOU UTTER CRETIN ! A Class **A**
push-pull output stage will do that too.

AB operation has NOTHING to do with distortion cancellation.


But it does. There is partial cancelation of 2H currents up until cut
off in one device,
and in each wave of signal voltage.

However, despite the very non linear **currents** in each PP device when
in AB,
the net voltage & current when summed in the load is substantially
linear.

The equivalent circuit of a PP pair is that of two non linear current
generators in series with each end of the
RLa-a. The summed current in Rla-a is linear.

But you can also have PP action and class B where the devices are in
parallel and working on a common load.


There us more than one way to set up devices in PP...

Patrick Turner.


Your problem is that you don't understand what you'r reading so you quote out of
context as a result of your utter IGNORANCE.

Graham

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Default Output classes A and AB



Patrick Turner wrote:

Eeyore wrote:
Andre Jute wrote:
Poopie Stevenson aka Eeyore wrote:
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.

Now this poor dumb slow learner Poopie Stevenson, an embarrassment to
everyone who comes into contact with him, claims to know more than the
RDH4! Yo, Poopie, in the RDH4 (Newnes 1997) on p 545 we find this
nugget of authoritative information by F. Langford-Smith B.Sc. B.E.
himself:

"Class AB operation indicates overbiased conditions, and is used only
in push-pull to balance out the even harmonics."


It's the push-pull that cancels those harmonics YOU UTTER CRETIN ! A Class **A**
push-pull output stage will do that too.

AB operation has NOTHING to do with distortion cancellation.


But it does.


ONLY because AB working is by design push-pull. The same thing happens in long-tailed
pairs. the distortion cancellation is NOTHING whatever to do with AB operation.

Graham



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John Byrns John Byrns is offline
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Default Output classes A and AB

In article ,
Patrick Turner wrote:

Cancelation of even order harmonics occurs in amps working in class AB
during that part of the wave forms which are in class A, ie, the bits
either side
of the zero crossing.

But once each tube moves into cut off, nothing is cancelled.


Patrick, I'm surprised to hear you say this. What are you trying to
tell us, that the even order harmonics are only cancelled during those
parts of the cycle when both tubes are conducting, but that the even
order distortion components reappear during those parts of the cycle
when only one tube is conducting? If you actually believe that you
should go back to the books and study the theory of harmonic distortion
more carefully. I hope you didn't get this notion from the RDH4, I
haven't read the RDH4's harmonic distortion explanation, but if this is
what it says I have just lost any respect I had for the book. In a
perfectly balanced PP amplifier the even order harmonic distortion is
completely cancelled even when the tubes are cut off for parts of the
cycle. It sounds like you have become one of Multi-grid's sock-puppets.

The two non linear current waves in the tubes of the AB pair
are summed, and the VOLTAGE total is substantially linear, with a small
fraction of the
THD of each tube's current wave.


And that small fraction is very small indeed, approaching zero to be
precise, for the even harmonics.

Its magic, but it works for most ppl.


It's not magic, it's just math.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/
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Eeyore Eeyore is offline
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Default Output classes A and AB



John Byrns wrote:

Patrick Turner wrote:

Cancelation of even order harmonics occurs in amps working in class AB
during that part of the wave forms which are in class A, ie, the bits
either side of the zero crossing.

But once each tube moves into cut off, nothing is cancelled.


Patrick, I'm surprised to hear you say this. What are you trying to
tell us, that the even order harmonics are only cancelled during those
parts of the cycle when both tubes are conducting, but that the even
order distortion components reappear during those parts of the cycle
when only one tube is conducting? If you actually believe that you
should go back to the books and study the theory of harmonic distortion
more carefully. I hope you didn't get this notion from the RDH4, I
haven't read the RDH4's harmonic distortion explanation, but if this is
what it says I have just lost any respect I had for the book. In a
perfectly balanced PP amplifier the even order harmonic distortion is
completely cancelled even when the tubes are cut off for parts of the
cycle.


I'd love to know how that happens. There's no cancellation of ANYTHING once one
side has ceased conducting !

Graham

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Don Pearce Don Pearce is offline
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Posts: 2,726
Default Output classes A and AB

On Thu, 25 Oct 2007 15:40:55 +0100, Eeyore
wrote:



John Byrns wrote:

Patrick Turner wrote:

Cancelation of even order harmonics occurs in amps working in class AB
during that part of the wave forms which are in class A, ie, the bits
either side of the zero crossing.

But once each tube moves into cut off, nothing is cancelled.


Patrick, I'm surprised to hear you say this. What are you trying to
tell us, that the even order harmonics are only cancelled during those
parts of the cycle when both tubes are conducting, but that the even
order distortion components reappear during those parts of the cycle
when only one tube is conducting? If you actually believe that you
should go back to the books and study the theory of harmonic distortion
more carefully. I hope you didn't get this notion from the RDH4, I
haven't read the RDH4's harmonic distortion explanation, but if this is
what it says I have just lost any respect I had for the book. In a
perfectly balanced PP amplifier the even order harmonic distortion is
completely cancelled even when the tubes are cut off for parts of the
cycle.


I'd love to know how that happens. There's no cancellation of ANYTHING once one
side has ceased conducting !

Graham


Because if you add an even harmonic to a signal, you have to make it
asymmetrical. You always get a peak coinciding with a trough on one
half cycle, followed by a peak coinciding with a peak on the next. If
you modify the signal to remove any asymmetry, you must by definition
remove the even harmonics.

d

--
Pearce Consulting
http://www.pearce.uk.com
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Arny Krueger Arny Krueger is offline
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Posts: 17,262
Default Output classes A and AB


"Patrick Turner" wrote in message
...

In class AB, each man pulls the saw about 1/2 way across the stroke then
lets go,
and the other guy grabs his saw handle and pulls the saw back the other
way.
Each man only mainly pulls the saw in turn, and applied force is jerky,
and frankly,
a difficult way to work; the Union will be down soon to have a go at the
boss who told
the men to saw the log that way.


So speaks someone who obviously has no experience cutting wood with a
cross-cut saw. You can pull on a saw, but pushing on it can easily cause it
to bend and bind. When 2 men use a cross-cut saw, each man pulls far more
than he pushes.

Class AB verging on pure class B is the preferred mode of operation for a
cross-cut saw.


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