Output classes A and AB
 

In article .com,
Andre Jute wrote:

On Oct 25, 7:40 am, 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

Holy ****! Did I say yet that Poopie is ignorant and incompetent?

Nah, nobody can be that stupid and uninformed about tube basics.

There are a lot of "stupid and uninformed" people around, there are at
least three people involved in this discussion that have expressed this
same belief as Eeyore, they are Multi-grid, Patrick Turner, and Eeyore.


Regards,

John Byrns

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

Output classes A and AB
 

On Oct 25, 4:16 am, "Arny Krueger" wrote:
"Don Pearce" wrote in message
Andre Jute wrote:
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.

Do you just lie from habit, Krueger, or are you incapable of using the
contents list or the index of a reference book?

The reference is from RDH4, Chapter 13, Section 1 (ii) Classes of
Operation.

Unsigned out of contempt

Output classes A and AB
 

"John Byrns" wrote in message
...
In article ,

"Arny Krueger" wrote:

Actually, there is cancellation regardless of whether one side has ceased
conducting or not, because the cancellation comes from the fact that the
transfer functions of the two sides are identical but opposite.

During the portion of the wave where both sides conduct, there may be
cancellation of odd order distortion.

Are you sure about this? yes.

This looks about right:

http://dave.uta.edu/dillon/ee5301/lecture11.htm


In school I was taught the law of half-wave symmetry. Any wave, no matter
how distorted, that has matching halves has no even-order distortion.

Aren't there two symmetry laws, I can never remember the second one, or
is it the first?

Thanks for the memory jog. Please see the reference. There are lots of
symmertry laws!

A wave that is composed of one half of any kind and the other half is
zero,
has only even-order distortion.

Could you say that again please?

A wave that is composed of one non-zero half wave of any kind, and the other
half is nothing (zero),
has only even-order distortion.

Output classes A and AB
 

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

Andre Jute wrote:

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 ********.

Even when I'm right? Tsch, tsch, Poopie. That's not even an original
thought. Ron Bales had it first.

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

You're blowing smoke through your fat arse, Poopie. That reference
doesn't say anything about "under any signal condition." Even
Wikipedia isn't as misinformed as you are. That must be a new record
for you.

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

It still wasn't me who said "under any signal condition". It is still
you who sstupidly said "under any signal condition", thereby voiding
the rest of the definition of Class A operation.

Graham

You're a clown, Poopie. Wiki in, Poopie out. Same as GIGO.

Unsigned out of contempt

Output classes A and AB
 

On Oct 25, 2:12 am, Eeyore
wrote:
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 ?

You do rather make a habit of being wrong, Poopie. Even your mother
noticed that.

Ever consided we might actually be right ?

Of course I have. I am a connoisseur of unlikely and bizarre events.
If you are ever unequivocally right in an argument with me, I get to
win a couple of thousand Euro that I've bet on the statistically
probability that nobody can be wrong *all* the time. Why, even a
broken clock shows the right time twice every day!

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

No point in abusing me, Fatso; it won't make me any less right or you
any less wrong.

Graham

AKA Poopie for a good reason. Why don't you share it with us. The
reason for your name is surely the one thing you do know.

Hey, Poopie, aren't you the same Graham Stevenson clown who announced
three or four years ago that he came to RAT "to be on Jute's arse".
You will let me know when you start, won't you.

Andre Jute
Rodeo rider

Output classes A and AB
 

On Oct 25, 1:17 pm, John Byrns wrote:
In article .com,
Andre Jute wrote:



On Oct 25, 7:40 am, 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

Holy ****! Did I say yet that Poopie is ignorant and incompetent?

Nah, nobody can be that stupid and uninformed about tube basics.

There are a lot of "stupid and uninformed" people around, there are at
least three people involved in this discussion that have expressed this
same belief as Eeyore, they are Multi-grid, Patrick Turner, and Eeyore.

From Eeyore (Poopie Stevenson) I expect only the worst; he says
whatever comes into this head as the opposite of what is said by
someone he dislikes, without any reference to the facts in
electronics; I have made a separate thread to illustrate that Poopie
is joined in this perversity by Pearce and Krueger.

I've given up reading Cuddles Multi-grid's posts; it is too wearing to
think up new ways of explaining the same simple thing to him over and
over again.

Patrick is entitled to a mistake now and again; he makes so few. I saw
the above and knew you would call him on it, so I read on before I
wasted my own time telling Patrick he'd better explain himself -- and
there you were, pointing out the faux pas. Actually, I regret that
Patrick is both honest and not as slippery with words as some we have
seen here, or we could have had a dingdong as he tried to explain it
away without admitting he was wrong. I expect he will just say he
slipped up.

I actually find Patrick's total ignorance of woodsawing the most
amazing thing in this thread -- especially considering that we have a
fellow with real expertise (and ruler braces) on board RAT: Iain
Churches.

Regards,

John Byrns

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

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

Don's limp driver Output classes A and AB
 

On Oct 25, 10:29 am, (Don Pearce) wrote:
On Thu, 25 Oct 2007 13:43:56 GMT, John Byrns
wrote:

In article ,
(Don Pearce) wrote:

Can you overdrive a class A amp to cutoff?

Yes, it is painfully easy.

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.

No, the coupling capacitor charges up as a result of grid current
shifting the bias point so that cutoff becomes even easier.

There is no
circumstance in which I have ever managed to put a class A amplifier
output device into cutoff.

You haven't tried very hard then.

The designs I have used must have been better matched in drive level
between the driver and output stages. They tended to limit almost
simultaneously so that the drive level to the output stage did not go
on rising as the input signal increased, just squared off. As I say, I
never saw an output valve go into cutoff.

d
--
Pearce Consultinghttp://www.pearce.uk.com

A driver stage that limp must be fertile ground for Miller, so how's
your bandwidth, Don?

Andre Jute
Lateral thinker and skunk-trapper

Output classes A and AB
 

In article ,
"Arny Krueger" wrote:

"John Byrns" wrote in message
...
In article ,

"Arny Krueger" wrote:

Actually, there is cancellation regardless of whether one side has ceased
conducting or not, because the cancellation comes from the fact that the
transfer functions of the two sides are identical but opposite.

During the portion of the wave where both sides conduct, there may be
cancellation of odd order distortion.

Are you sure about this? yes.

This looks about right:

http://dave.uta.edu/dillon/ee5301/lecture11.htm

Which type of symmetry discussed in that lecture is suggestive of
canceling odd order distortion? Some of the cases presented appear to
have a period of T/2 rather than T which confuses the issue. Also I am
assuming that the output devices in our idealized amplifier have a
single valued input to output function, which somewhat constrains the
types of symmetry the output signal can have.

In school I was taught the law of half-wave symmetry. Any wave, no matter
how distorted, that has matching halves has no even-order distortion.

Aren't there two symmetry laws, I can never remember the second one, or
is it the first?

Thanks for the memory jog. Please see the reference. There are lots of
symmertry laws!

A wave that is composed of one half of any kind and the other half is
zero,
has only even-order distortion.

Could you say that again please?

A wave that is composed of one non-zero half wave of any kind, and the other
half is nothing (zero),
has only even-order distortion.

You took me too literally, I wondered if you would and left the question
so it would allow simply saying it again. If you actually mean what you
seem to be saying, you are wrong, as a trivial example will easily
demonstrate. Or are you talking about the wave from each of the two
devices, which is why I asked for clarification?


Regards,

John Byrns

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

Output classes A and AB
 

Eeyore wrote:

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.

Well, sure, LTP low 2H output relies on each device having its own 2H
cancelling
with the other one. They cannot work in class AB as neither of them can
cut off, because of the large
common cathode resistance.
But in a power output stage, there IS in effect a large LTP working
until
one tube does cut off, ie, have Ia less than 1/10 the idle value, and
then the
cancelation is zero, but the voltage output is the sum of two devices
acting
non linearly upon each +ve and -ve 1/2 waves.

In fact one can set up an output pair of tubes with a commonened cathode
constant current sink,
and have the output stage ONLY able to work in class A, and if one tube
cuts off
there is no output in the anode circuit connected to the OPT with CT.

Such a class A output stage has been touted as being the purest form of
class A PP by Allen Wright.
It can be driven by having SE drive to one grid of the PP pair with the
other grid gounded.
I have used the principle for driver stages.

Patrick Turner.
d

for the CCS as the common cathode e


Graham

Output classes A and AB
 

John Byrns wrote:

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?

In effect the even order distortions DO re-appear when the amp moves to
class AB.

Its because of the mismatch between the two tubes, and each has slightly
or greatly different gm, so each +ve and -ve half of the waves are
amplified
by a different amount, and hence you get even order generated in the
output from across the whole primary
or secondary of the OPT.
The odd order is also there, and usually dominates the distortion
profile,
so that in a typical 45 watt amp using a pair of EL34 in UL and class
AB, there might be
very low 2H in the first 5 watts, but just below clip its 1%, and with
maybe 4% 3H.


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.

Not enough ppl have taken their own measurements
of typical amplifiers to know as much as what is written in RDH4 by
demonstrating
it all to themselves.

PP amps have much lower 2H at all levels than the same tubes used in SE
parallel.
But 2H IS produced due to tube mismatches.
But I have used tubes which are well matched and 2H is sometimes very
low right up to clipping,
and usually the 3H is at least 15dB greater.

But in old amps where the tubes ahve aged, 2H in PP amps can be as great
as 3H, and this is easy
to find in such amps as Quad-II, where the old input pair of pentodes
has a large differential 2H content,
and so does the unmatched KT66, and reversing positions of the input
pair will
either cancel or add to the 2H and the difference in 2H after such tube
swaps can be 15dB.


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.

Its magical luck if you have well matched output tubes.
The math is used to describe it only...

Where you have a fixed bias PP amps and a pair of 10 ohm R as series
cathode
resistors, you can see the curent waves on the CRO by monitoring voltage
across each 10 ohms.
At high AB PO, the wave looks like that of a half wave rectifier.
if you connect a 1:1 transformer from cathode to cathode, the secondary
voltage
looks fine. Its a sine wave but with many harmonics at low level like
the anode to anode signal voltage,
except that it increases with a lower load and is thus a source of
current FB voltage
and can be used as positive current FB to reduce Rout.
(( There are bothers with a set up like this because this increases
THD/IMD,
but with NFB used as well the THD/IMD can be much reduced, but Rout made
to be
very low, or near 0.0 ohms, or even negative..))

Patrick Turner.



Regards,

John Byrns

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