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Output classes A and AB

In article ,
"Rudy" wrote:

for the purpose of loadline analyses, that is a fair approximation.
for analyzing the actual working mechanism, it lacks accounting for
the element of time, as the transformer actually stores energy
comparable to a fast rotating heavy object storing rotational impulse
so in case a tube is cutoff, it's plate will happily follow to wherever
that winding will take it.
(well, not so happy when certain V's are exceeded, perhaps:)

Huh, wouldn't the transformer store energy more like a spring does,
after all the schematic symbols are very similar?

If "the transformer actually stores energy comparable to a fast rotating
heavy object" wouldn't that cause a 6 dB/octave roll-off, resulting in a
serious loss of high frequencies?

Regards,

John Byrns

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

Output classes A and AB

"John Byrns" wrote in message
...
: In article ,
: "Rudy" wrote:
:
: for the purpose of loadline analyses, that is a fair approximation.
: for analyzing the actual working mechanism, it lacks accounting for
: the element of time, as the transformer actually stores energy
: comparable to a fast rotating heavy object storing rotational impulse
: so in case a tube is cutoff, it's plate will happily follow to wherever
: that winding will take it.
: (well, not so happy when certain V's are exceeded, perhaps:)
:
: Huh, wouldn't the transformer store energy more like a spring does,
: after all the schematic symbols are very similar?
:
: If "the transformer actually stores energy comparable to a fast rotating
: heavy object" wouldn't that cause a 6 dB/octave roll-off, resulting in a
: serious loss of high frequencies?
:
:
: Regards,
:
: John Byrns
:
err, yes, i just wanted to emphasize the
'flux doesn't stop on a dime' aspect.
:-)
Rudy

Output classes A and AB

On Oct 31, 4:46 pm, John Byrns wrote:
In article ,

"Rudy" wrote:
for the purpose of loadline analyses, that is a fair approximation.
for analyzing the actual working mechanism, it lacks accounting for
the element of time, as the transformer actually stores energy
comparable to a fast rotating heavy object storing rotational impulse
so in case a tube is cutoff, it's plate will happily follow to wherever
that winding will take it.
(well, not so happy when certain V's are exceeded, perhaps:)

Huh, wouldn't the transformer store energy more like a spring does,
after all the schematic symbols are very similar?

If "the transformer actually stores energy comparable to a fast rotating
heavy object" wouldn't that cause a 6 dB/octave roll-off, resulting in a
serious loss of high frequencies?

Regards,

John Byrns

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

Yes it does. This is from the leakage inductance. Things come to a
complete stop when leakage L and capacitance resonate...:)
cheers,
Douglas

Output classes A and AB

In article .com,
Multi-grid wrote:

On Oct 31, 4:46 pm, John Byrns wrote:
In article ,

"Rudy" wrote:
for the purpose of loadline analyses, that is a fair approximation.
for analyzing the actual working mechanism, it lacks accounting for
the element of time, as the transformer actually stores energy
comparable to a fast rotating heavy object storing rotational impulse
so in case a tube is cutoff, it's plate will happily follow to wherever
that winding will take it.
(well, not so happy when certain V's are exceeded, perhaps:)

Huh, wouldn't the transformer store energy more like a spring does,
after all the schematic symbols are very similar?

If "the transformer actually stores energy comparable to a fast rotating
heavy object" wouldn't that cause a 6 dB/octave roll-off, resulting in a
serious loss of high frequencies?

Regards,

John Byrns

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

Yes it does. This is from the leakage inductance. Things come to a
complete stop when leakage L and capacitance resonate...:)

We specify a well designed and wound transformer with low leakage
inductance so that it doesn't cause high frequency roll-off problems
until well above the audio range. The impact of excess leakage
inductance is also minimized by using a pentode output tube, which given
your name I am sure you know all about.

Regards,

John Byrns

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

Output classes A and AB

Rudy wrote:

"Patrick Turner" wrote in message
...
:
:
: Rudy wrote:
:
: "John Byrns" wrote in message
: ...
: : In article .com,
: : Andre Jute wrote:
: :
: : On Oct 25, 7:40 am, Eeyore
: : wrote:
: :
: : 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
:
: it seems the error made is in using the wrong mental model, that is
: seeing the transformer primary as a resistance.
:
: To the vacuum tubes, RLa-a IS a resistance.

for the purpose of loadline analyses, that is a fair approximation.
for analyzing the actual working mechanism, it lacks accounting for
the element of time, as the transformer actually stores energy
comparable to a fast rotating heavy object storing rotational impulse
so in case a tube is cutoff, it's plate will happily follow to wherever
that winding will take it.
(well, not so happy when certain V's are exceeded, perhaps:)

The analogy is fine, as long as you remember there is no such thing as
momentum
in electronics.

the output result will just be more or less symmetrically compressed,
3H, 5H, etc.

this is distinctly different from a transistor PP, mostly apparent
when you think of asymmetrical signals (music) driving it ;-)

Asymetrical music signals will still have a dc content of zero,
and there's very nearly always equal energy each side of zero.

In a bjt output stage or a tube stage where the load is taken from the
junction of
the two output bjts or tubes, the Fourier waves are shunting one
another,
rather than being applied common mode as John B is so adament about.

If one device is omitted, the class B waves are like you get with an SE
tube
biased on the brink of cut off.

the load each PP tube sees is not suddenly changed at cutoff,
it is in fact only balanced somewhat is a small region around the
bias point, as with larger swing the dynamic plate resistance
will vary more between the tubes, 3H will start to appear

a measure of 'true class A' power of an AB pp, meaning
the 3H would be low without nfb, would be the region where
current is below twice the bias and cutoff AND dynamic
plate R of the output tubes doesn't change more than
"X" percent.

Hmm, a little hard to follow you, but while a tube is cut off there
is *no load* connected to it, unless in other words we say the Fourier
currents all add to zero current for
1/2 a wave and are flowing in tube and 1/2 the OPT, but are conveniently
summing to 0.0amps dc or ac for
that 1/2 cycle.

Usually 3H is HIGH witout NFB and unacceptably high when tubes are
biased for class B at low levels,
then as PO increases the % reduces, then inceases again near clipping.

This was a problem with early SS amps; the early designers didn't know
how to deal with
the SS distortions at low levels where tube amps at the same level were
much freer from distortions,
and spectra was benign.

The early designers could not afford to have hot idling class AB stages
because germanium transistors
went phut all too easily when they got hot.
So they were forced int making all their crummy creations using class B
working,
and with token idle current.

Bean counters made damn well sure OPTs were damn well eliminated from
the SS amps
during the transition from tubes to SS. For awhile, input transformers
on SS amps were used because of the
appallingly low base input resistance of the early power transistors,
and besides,
there were lots of out of work OPT winders available to wind simpler
cheap IPT for SS
to fill them in until permanent retrenchment, retirement or the sack.

The appalling design ideas carried over into the days of early silicon
bjts which turned out
to be much more rugged than the germanium types.

But SS heralded the use of class B, and the use of ever increasing
amounts of NFB,
so that we have amps with 40dB of local series voltage NFB in the form
of emitter follower connection,
and another 60dB of global NFB, to crossover distortion is difficult to
identify as a spurious artifact
amoungst the macro 3H and 2H which dominate the THD spectra just below
clipping,
but which rarely exceed 0.005% if the designer knows his stuff.

In effct, many VAS stages in SS amps are merely a gain bjt with CC
collector load to power
a relaetively high impedance base input impedance of darligton output
stage device arrays.
The Single Ended VAS stage often has gain = 5,000x, and THD of this
stage is say 5% at say
25Vrms, mainly 2H and 3H, very much like a pentode's spectra. The VAS
stage THD well exceeds the
output stage THD because of the emitter follower NFB.
The 60dB of global NFB reduces the 5% of VAS thd to 0.005%.

Because tubes have lower gain when used in audio circuits than available
with bjts,
and because of stability reasons, a large amount of NFB cannot be
applied, with a total of 40 dB being about the limit.

Patrick Turner.

... to be discussed,
heh,

Rudy

:
: One R set up set up with a CT so any signal voltage applied between the
: end and the CT
: is applied in opposite phase to the other end, courtesy of the action of
: the transformer.
:
: Its RL a-a.
:
: This transformed single R appears to the tubes somewhat variably.
: In class B, while a tube is conducting, the load on the tube is 1/4
: RLa-a,
: and when both conduct in class A the load on each tube is 1/2RLa-a.
:
: The secondary R load is always reflected to the two tubes as RLa-a, with
: a CT.
: The Ra of the tubes seen at the secondary varies.
:
: Say you have Ra = 1.2k for EL34 in triode, and 6k:6 ohms OPT. ZR =
: 1,000:1
: In class A, Ra-a = 2.4k and is transformed to 2.4ohms by the OPT.
: In class B, only one tube is connected via 1/2 the primary, so only one
: Ra = 1.2k
: and OPT Z ratio has changed to 1.5k:6, because 1/2 the OPT primary isn't
: operating
: because one tube is cut off, so turn ratio is halved, Z ratio Ra in
: class B = 1.5k/6 = 250,
: so Ra at the output = 1.5k/250 = 6 ohms.
:
: The Rout of the amplifier at the sec is Ra transformed, and notice the
: change in Rout
: between A and AB. Its responsible for major 3H, 5H and other
: distortions.
:
:
:
: sure, PP operating on a pure R load would cease to
: cancel when one side would be cutoff, as it would no longer
: partake in the transfer curve for PP !
: with a transformer, however, the transfer curve is a function
: of the tight coupling of the primary halves, so always PP ;-)
: (not the current, but the core flux is what matters)
:
: If one runs a class B PP amp with only ONE output tube,
: you will get a badly distorted signal like the one you'd get
: with a pure un-magnetically coupled R between B+ and the anode,
: only at each end of the OPT pri there would be two phases of the same
: distorted signal.
: The load with one tube and OPT is the same as with a single R taken to a
: suitably higher B+
: than used with an OPT.
:
: Fourier could describe what harmonics flow all the time despite cut off.
:
: Furious arguemnts have followed about him.
:
: Patrick Turner.
:
:
: Rudy

Output classes A and AB

John Byrns wrote:

Rudy wrote:

for the purpose of loadline analyses, that is a fair
approximation.
for analyzing the actual working mechanism, it lacks
accounting for
the element of time, as the transformer actually stores
energy
comparable to a fast rotating heavy object storing
rotational impulse
so in case a tube is cutoff, it's plate will happily
follow to wherever
that winding will take it.
(well, not so happy when certain V's are exceeded,
perhaps:)

: Huh, wouldn't the transformer store energy more like a
spring does,
: after all the schematic symbols are very similar?

A capacitor is analogous to a spring. Don't be fooled by the
symbols. A resistor is analogous to a damper, incidentally.

: If "the transformer actually stores energy comparable to
a fast rotating
: heavy object" wouldn't that cause a 6 dB/octave
roll-off, resulting in a
: serious loss of high frequencies?

Low frequencies, considering the mass is in shunt. Yes, it
does.

The concept of momentum in electronics is a bit interesting.
Is LI concerved?

If I have a perfect inductor passing current in a loop, and
switch a second, equal, inductor into the circuit in series
with the first, will the current be halved? If instead I
double the inductance by inserting a core into the first
inductor, will the current be also halved? In both cases
large voltages would accompany the change, analogous to
collision forces.

Ian

Output classes A and AB

In article ,
"Ian Iveson" wrote:

John Byrns wrote:

Rudy wrote:

for the purpose of loadline analyses, that is a fair
approximation.
for analyzing the actual working mechanism, it lacks
accounting for
the element of time, as the transformer actually stores
energy
comparable to a fast rotating heavy object storing
rotational impulse
so in case a tube is cutoff, it's plate will happily
follow to wherever
that winding will take it.
(well, not so happy when certain V's are exceeded,
perhaps:)

: Huh, wouldn't the transformer store energy more like a
spring does,
: after all the schematic symbols are very similar?

A capacitor is analogous to a spring. Don't be fooled by the
symbols. A resistor is analogous to a damper, incidentally.

It depends on which dual you are using, an inductor can also be
analogous to a spring and a capacitor to a mass.

Regards,

John Byrns

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

Output classes A and AB

On Thu, 01 Nov 2007 12:26:01 -0500, John Byrns
wrote:

In article ,
"Ian Iveson" wrote:

John Byrns wrote:

Rudy wrote:

for the purpose of loadline analyses, that is a fair
approximation.
for analyzing the actual working mechanism, it lacks
accounting for
the element of time, as the transformer actually stores
energy
comparable to a fast rotating heavy object storing
rotational impulse
so in case a tube is cutoff, it's plate will happily
follow to wherever
that winding will take it.
(well, not so happy when certain V's are exceeded,
perhaps:)

: Huh, wouldn't the transformer store energy more like a
spring does,
: after all the schematic symbols are very similar?

A capacitor is analogous to a spring. Don't be fooled by the
symbols. A resistor is analogous to a damper, incidentally.

It depends on which dual you are using, an inductor can also be
analogous to a spring and a capacitor to a mass.

Regards,

John Byrns

I haven't given this any thought, but my intuition says that when you
give an inductor a kick with a voltage, it is reluctant to get moving
(current flow), which makes it more like the mass. How would you
intuit that the other way?

d

--
Pearce Consulting
http://www.pearce.uk.com

Output classes A and AB