Output classes A and AB
 

Andre Jute wrote:

"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.

Ah yes, you're mired in the past. I suppose all technological development ceased
after publication of that tome.

Graham

Output classes A and AB
 

Andre Jute wrote:

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?

You're NOT right. Your ignorance is simply confusing you.

HOWEVER, to keep you happy I am happy to modify to modify my definition for clarity. I
already posted this once but I suppose you like to argue more than anything.

"the output device(s)never cease conducting *under any signal condition* within the rated
specification".

To be honest, to have to explicitly state "within the rated specification" is really a
case of pandering to fools, which certainly describes YOU, Jootikins.

Graham

Output classes A and AB
 

Andre Jute wrote:

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

If there was ever a case of projection !

Graham

Output classes A and AB
 

In article ,
Eeyore wrote:

John Byrns wrote:

(Don Pearce) wrote:
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 !


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.

Finally a man who understands the theory!

But it's not by ** CANCELLATION ** in the case of AB operation beyond the
crossover point. That's my issue with the description.

It does have that effect but the use of the word *cancellation* is wong IMHO.
There should be another way to describe it.

Cancelation is the right word, the two tubes, even when they, "operate
beyond the crossover point", generate harmonics which when added, add in
phase for odd harmonics, and out of phase for even harmonics, hence the
even harmonics "cancel" in the output. This is a very common meaning
for the word "cancellation", and I can't think of a better use for the
word. If it "does have that effect", then if it walks like a Duck and
Quacks like a Duck, it probably is a Duck.


Regards,

John Byrns

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

Output classes A and AB
 

John Byrns wrote:

In article ,
Patrick Turner wrote:

[Snip]

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.

Isn't 1.25k too low a load for getting maximum power from a KT88 in
triode mode, even in class B?

No.

If the RL a-a = 5k, then the class B load is 1.25k,
and if Ea = 500V, then max Ia at grid current is about 220mA.
If you run AB2, you get a heck of a lot more Ia up to around 350mA.
KT88 ca easily make 500mA, depending on loads etc.
One can get 140W from a pair in AB2 in tetrode.

But for hi-fi, about 25 watts max is about right, with RL about 8ka-a.


[Snip]

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.

What is all this talk about ARC's anyone else's rules that would keep
you from handing out free copies of their abominable concoctious junk,
assuming you drew the schematic your self? You mentioned this same
issue in connection with the ManleyLabs amplifier you modified, my
understanding is that they only have protection for schematics they have
drawn, if you draw your own schematic of the same circuit, they have no
rights with regard to it. Any Lawyers out there care to comment?

I fell OK about just letting folks know what they could do
to rebuild a Manley or ARC or start from scratch and use the schematic I
will be posting
at my site.
There is nothing I can gain by posting a copy of the original schematic
these companies use.
Many companies do NOT like ppl posting copies of their schematics on the
web,
and I have no intention of offending them by doing so.
I am free to post alternative schematics used in the cases of their amps
though,
and Manley and ARC would do very well to copy
the schematics for their own use in future. They'd be welcome afaiac,
but I betcha they wouldn't
dream of doing it, because then they'd appear to those in the know that
they don't know
more than I do, and if you asked them, they'd get a bit pooey about it
all
and of course ARC et all know what is the best way to make an amp they'd
say.

ARC and all these companies would never admit to the follies of their
designs.
They really don't like ppl questioning why. They like blind praise it
seems to me.

They say that once you alter anything there isn't any more support.
OK, I can cope with that. I improve their amp's function, and company
help to support
their original design will not be required.
Why would I tell my customers that we ought to keep things original
to get support to ensure toubles keep happening?

Big US companies like to have a stranglehold on service and parts supply
after you've bought an amp of theirs.
I'd rather not trouble them, and I like to go my own way.
I admire their success which I cannot ever attain and I hope they find
all I say is food for thought.



[Snip]

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.

Is this on the 4 Ohm tap? If so it is only 66 dB below 1 Watt, or 69 dB
with an 8 Ohm speaker connected to the 4 Ohm tap, not an awe inspiring
result, but apparently typical for many tube amps. But maybe it's not
so bad with the preamp included, did you measure the hum&noises of the
VT100 alone?

After putting in a CLC type B+ filter and re-routing all the earth
paths,
and fimally reducing hum to less than 1mV, I was satisfied.
The original had lots of noise in SE input mode.
with both the inputs grounded, the noise of the power amp was very low;
and the simple test is that with 89dB/W/M sensitve speakers, you don't
hear ANY noise
unless you place your ear against a speaker, and all there should be is
a slight hiss,
and perhaps barely detectable background buzz.
My DVM reads 0.00Vrms when placed on the outputs, and with the preamp
connected and in SE feed to the power amp, with gain turned up fully,
noise was so low I had to put an ear to the spekers to hear any.
The DVM reads 0.00Vrms which occasional flicker reading to 0.001Vrms.

Noise may increase somewhat when music flows in the amps, but not much
at the few watts
which will be used.
If noise is say 0.5mV, and average power levels are 1Vrms, the
unweighted SNR = -66dB.
This seems like a hopelessly poor figure, but its a typical figure
better than what many
commercial SS and tube amps make.
At 30Vrms, if noise is still 0.5mV, then the SNR gets a lot better at
-96dB approx.
What people really want is an amp so quiet that NO noise is present even
when they walk over close to the
stand to adjust volume etc.
This allows them to listen at low levels.

The loudest noise I get is from the darn power transformer in the VT100,
audible from 3 feet away.

Patrick Turner


Regards,

John Byrns

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

Output classes A and AB
 

John Byrns wrote:

Eeyore wrote:
John Byrns wrote:
(Don Pearce) wrote:
Eeyore wrote:

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


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.

Finally a man who understands the theory!

But it's not by ** CANCELLATION ** in the case of AB operation beyond the
crossover point. That's my issue with the description.

It does have that effect but the use of the word *cancellation* is wong IMHO.
There should be another way to describe it.

Cancelation is the right word,

********.


the two tubes, even when they, "operate beyond the crossover point",

When one tube has ceased conducting, there's NOTHING TO CANCEL, you IGNORANT
****WITTED ****.

CANCELLATION IS THE *** WRONG WORD ***.

In fact it's ADDITION of waveforms, not cancellation.

Graham

Output classes A and AB
 

John Byrns wrote:

In article ,
Patrick Turner wrote:

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.

You are changing your tune a bit, you originally said "once each tube
moves into cut off, nothing is cancelled",

One cannot have distortion cancelling by one tube cancelling that in
another
when one is cut off. But the SUM of the joint action of each tube in
class AB with very non linear currents
gives a linear voltage outcome.


now you say "Its because of
the mismatch between the two tubes", which is a completely different
deal.

In class A, you often do not get perfect 2H cancellations, since tubes
are not matched,
so 2H is present with 3H etc.
The effect of missmatched tubes gets worse when the amp moves to AB.
more 2H with more of everything else. Summing of the output voltage
still occurs while little cancellation happens.

I stated in several of my posts that the tubes must be identical,
of course that is impossible in the practical world, but we want to get
as close as possible if we are intent on minimizing distortion. When
the tubes are mismatched, the problem is not just confined to class AB
operation, it will occur even in a class A amplifier with mismatched
tubes.

That is what I have said all along. PP isn't perfect.
Tubes and bjts and mosfets ain't perfect.
SS pn and pnp devices are often about as similar as using a 6L6 and EL34
in a tube PP amp; ie, not very well matched.
Doesn't madder, add piles of NFB and she'll be right....

The bias may be able to be adjusted to cancel the 2 nd harmonic
at some selected power output, but there is no guarantee that the other
even harmonics will also be canceled, even in a class A amplifier if the
tubes are mismatched, and if the power output level is changed even the
second harmonic can reappear with mismatched tubes. It is the
mismatched tubes that are at the root of the problem, not operating in
the class AB region with the tubes cut off over part of the cycle.

Matched tubes don't stay matched. One should not be too dependant on
matched tubes.
In a class AB amp with 50% of the power in class A before AB commences,
and with tubes with 10% gm variation, the amount of 2H in the first few
watts is way less than if the tubes were operating
in SE mode.

One does not have to worry if the TD in an AB a tube is below 0.1% at 2
watts.
The 2H and 3H will be dominant, and not cause undue IMD.

if the same amp makes 50 watts in AB, and THD is 0.5%, then its OK,
still not to bad,
but nodody will notice it.

I like having less than 0.05% for everything below average levels; if
for an instant during a drum beat
power rises to an instant 50 watt level, and the THD leaps to 0.5%, I am
not concerned.

Most of my PP amps have less than 0.25% at clipping and 0.03% at average
levels.

I have heard a VAC amp with 4 x 300B in PP for each channel to make 56
watts max,
and its usable with/without global NFB.

There is no difference to the sound that I am aware of when altering NFB
from zero to
having 9db applied. This means that if the THD is 0.1% with zero NFB,
applying 9dB to reduce it to about 0.03% makes no audible difference to
me.

Patrick Turner.




Regards,

John Byrns

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

Output classes A and AB
 

In article ,
Patrick Turner wrote:

John Byrns wrote:

In article ,
Patrick Turner wrote:

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.

Isn't 1.25k too low a load for getting maximum power from a KT88 in
triode mode, even in class B?

No.

If the RL a-a = 5k, then the class B load is 1.25k,
and if Ea = 500V, then max Ia at grid current is about 220mA.
If you run AB2, you get a heck of a lot more Ia up to around 350mA.
KT88 ca easily make 500mA, depending on loads etc.
One can get 140W from a pair in AB2 in tetrode.

But I was asking about the best load for a class B triode amp, is 1.25k
too low for a KT-88? I guess I will have to see if I can find the
triode plate curves for the KT-88, or maybe I can substitute the 6550
curves.

What is all this talk about ARC's anyone else's rules that would keep
you from handing out free copies of their abominable concoctious junk,
assuming you drew the schematic your self? You mentioned this same
issue in connection with the ManleyLabs amplifier you modified, my
understanding is that they only have protection for schematics they have
drawn, if you draw your own schematic of the same circuit, they have no
rights with regard to it. Any Lawyers out there care to comment?

I fell OK about just letting folks know what they could do
to rebuild a Manley or ARC or start from scratch and use the schematic I
will be posting
at my site.
There is nothing I can gain by posting a copy of the original schematic
these companies use.

I was not talking about the original schematic drawn by these companies,
I was talking about a schematic of the same circuit that you or anyone
else may have drawn, it is my understanding that there is nothing to
prevent you from legally posting such a schematic, illustrating the same
circuit as the company circuit, you just can't post the schematic drawn
by the company.

Many companies do NOT like ppl posting copies of their schematics on the
web,
and I have no intention of offending them by doing so.

I am not suggesting that you should do it, but it is my understanding
that they have no say in your posting a schematic you drew of their
circuit. Of course you are going to offend them by doing that, and they
may retaliate by denying you access to replacement parts.

I am free to post alternative schematics used in the cases of their amps
though,

You are also free to post your rendition of the schematic for their
original circuit. As I understand the situation they only have rights
to and control over their drawing of the original circuit, you are free
to create and distribute copies of a new drawing of the circuit that was
drawn by you.


Regards,

John Byrns

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

Output classes A and AB
 

Patrick Turner wrote:

One cannot have distortion cancelling by one tube cancelling that in
another when one is cut off.

THANK YOU !

Basics do matter.

Graham

Output classes A and AB
 

Patrick Turner wrote:

But the SUM of the joint action of each tube in
class AB with very non linear currents
gives a linear voltage outcome.

And should not be confused with genuine CANCELLATION of distortion by Class A
push-pull operation.

Graham