Voltage swing

[Lost'n Found]

Hello.

I am using PSPICE to simulate the output stage of a tube amplifier. I am
using a 420v DC and an output transformer.

The voltage on the plate of the tube swings between 840v and 420v. I know
that the output transformer opposses the current change, but I thought that
the voltage should swing up and below the 420v, not between 840v and 420v.

Is it operating correctly? I mean can the voltage swing between VDC Max and
higher?

thank you for your time.

[David R Brooks]

Lost'n Found wrote:
> Hello.
>
> I am using PSPICE to simulate the output stage of a tube amplifier. I am
> using a 420v DC and an output transformer.
>
> The voltage on the plate of the tube swings between 840v and 420v. I know
> that the output transformer opposses the current change, but I thought that
> the voltage should swing up and below the 420v, not between 840v and 420v.
>
> Is it operating correctly? I mean can the voltage swing between VDC Max and
> higher?
>
> thank you for your time.
>
Assuming you are using a single-tube, Class-A stage.
Yes, it should swing equally both ways.

[Patrick Turner]

David R Brooks wrote:

> Lost'n Found wrote:
> > Hello.
> >
> > I am using PSPICE to simulate the output stage of a tube amplifier. I am
> > using a 420v DC and an output transformer.
> >
> > The voltage on the plate of the tube swings between 840v and 420v. I know
> > that the output transformer opposses the current change, but I thought that
> > the voltage should swing up and below the 420v, not between 840v and 420v.
> >
> > Is it operating correctly? I mean can the voltage swing between VDC Max and
> > higher?
> >
> > thank you for your time.
> >
> Assuming you are using a single-tube, Class-A stage.
> Yes, it should swing equally both ways.

The actual swing in each direction with no load connected to the tube, ie, just
the choke with say 60mA of dc and with anode to cathode dc voltage = 420V
will depend on what sort of tube is being used.
If a triode is used the swing will be approximately equal going up or down from
the anode idle voltage,
maybe +/- 300V if the tube is an EL34 in triode.
The poster doesn't tell us any of the crucial information about his test
conditions then expects us
to answer a question.
He should read up about tube behaviour and what all the data curves mean and load
lines and
read about magnetics.
Perhaps he could choose a few pages from the list at
http://www.turneraudio.com.au/education+diy.html

If the tube he is using is in pentode mode and without a load connected
the upward swing of anode voltage when the grid goes so negative
as to cut off the Ia entirely will be much more than the swing down.

The pentode will have much dissimilar voltage swings in + or - directions because
of their inherent
distortion and lack of internal voltage feedback.

When loaded with various loads the tube distortion varies a lot.

Trying to get any simulation program to correctly simulate the much varied
distortion
spectra of an output pentode with loads between 1k and 10k would be rather
difficult.

I never simulate very much because its being bone lazy. I go to my workshop
and build the test circuit. I deal with REALITY BEHAVIOURS.


Patrick Turner.

[[email protected]]

Patrick Turner wrote:
>
> I never simulate very much because its being bone lazy. I go to my workshop
> and build the test circuit. I deal with REALITY BEHAVIOURS.
>
>
> Patrick Turner.

Hi RATs!

Yup. Simulations ain't what they sim ...

I only deal with fanciful misinterpretations. Truthfully listening to a
piece of paper wiggling in my crowded little Audio Dungeon may seem
Ideal to some crazy morons, but, basically, it would bore me more then
our resident non-thinkers. OK, maybe not more, sigh.

Somehow, I can transpose the joy of being in those symphony halls in
decades past to laying here listening to a couple of paper cones and
domes of doubtful heritage wiggling on as close to a single vector as
they can and feel that inner joy happen.

Simulations of these simulations may be cool if you are way hipper than
me, but, I just like being made a fool of at the immediate level. Call
me old fashioned.

As far as voltage is concerned, does anybody really know what zero
volts means? It may vary with where and how you measure.

We can teach computers to lie to us however we choose. Lying to
ourselves takes much more talent and suffers many more failures.

Get into this world. Build some goddam circuits and listen.

Then, we will patiently try to explain where you went wrong in your
choice of recordings ...

Happy Ears!
Al

[Eeyore]

" wrote:

> Patrick Turner wrote:
> >
> > I never simulate very much because its being bone lazy. I go to my workshop
> > and build the test circuit. I deal with REALITY BEHAVIOURS.
> >
> >
> > Patrick Turner.
>
> Hi RATs!
>
> Yup. Simulations ain't what they sim ...

WTF would you know ?

Graham

[Bob H.]

HI

Yes. The windings of the output transformer will store energy and then
release it, causing the voltage swing.

Bob H.

Lost'n Found wrote:
> Hello.
>
> I am using PSPICE to simulate the output stage of a tube amplifier. I am
> using a 420v DC and an output transformer.
>
> The voltage on the plate of the tube swings between 840v and 420v. I know
> that the output transformer opposses the current change, but I thought that
> the voltage should swing up and below the 420v, not between 840v and 420v.
>
> Is it operating correctly? I mean can the voltage swing between VDC Max and
> higher?
>
> thank you for your time.

[Eeyore]

"Bob H." wrote:

> HI
>
> Yes. The windings of the output transformer will store energy and then
> release it, causing the voltage swing.

It should swing 'either side' of the 420V B+.

Graham

[Patrick Turner]

Eeyore wrote:

> " wrote:
>
> > Patrick Turner wrote:
> > >
> > > I never simulate very much because its being bone lazy. I go to my workshop
> > > and build the test circuit. I deal with REALITY BEHAVIOURS.
> > >
> > >
> > > Patrick Turner.
> >
> > Hi RATs!
> >
> > Yup. Simulations ain't what they sim ...
>
> WTF would you know ?
>
> Graham

He knows enogh to get by I'd say; he knows hi-fi is all one big simulation.
Concert halls is where reality is, and once it comes via cone, its simulation.
And cool is cool, depending where you are, and how you like absolute zero volts,
or degrees K.

I prefer being at about 22 C, and have my speakers swing about 2.8V each side
of zero V, where this mysterious voltage is the nearby earth stake potential
at my place.

But I do examine the data sheets and when i look and plot a load line
it is a kind of simulation, but then I have to draw a real line, and read from real
plotted curves.
Then I hope to get what I see on the real bit of paper when I measure the real
circuit.

Al's cheerful despite his limitations, so no need to ask WTF this or that.

Patrick Turner.

[Patrick Turner]

"Bob H." wrote:

> HI
>
> Yes. The windings of the output transformer will store energy and then
> release it, causing the voltage swing.
>

This release of stored magnetic energy in the inductance of the choke or OPT is a
mysterious business.
Why does the signal usually closely follow the tube's commands when it rises
above the anode DC supply?

What happens if the flow of dc in the L is interupted in an extremely short time?

what stops the stored magnetic energy from producing a voltage rise that is
infinite?

Patrick Turner.


>
> Bob H.
>
> Lost'n Found wrote:
> > Hello.
> >
> > I am using PSPICE to simulate the output stage of a tube amplifier. I am
> > using a 420v DC and an output transformer.
> >
> > The voltage on the plate of the tube swings between 840v and 420v. I know
> > that the output transformer opposses the current change, but I thought that
> > the voltage should swing up and below the 420v, not between 840v and 420v.
> >
> > Is it operating correctly? I mean can the voltage swing between VDC Max and
> > higher?
> >
> > thank you for your time.

[Andre Jute]

Lost'n Found wrote:
> Hello.
>
> I am using PSPICE to simulate the output stage of a tube amplifier. I am
> using a 420v DC and an output transformer.
>
> The voltage on the plate of the tube swings between 840v and 420v. I know
> that the output transformer opposses the current change, but I thought that
> the voltage should swing up and below the 420v, not between 840v and 420v.
>
> Is it operating correctly? I mean can the voltage swing between VDC Max and
> higher?
>
> thank you for your time.

Hello, Lost:

It is most likely your simulation is somehow screwed. You don't give us
enough information to tell what it is you're doing, never mind where
you went wrong. What sort of tube are you simulating, in what sort of
topology, in what class of operation, and so on.

But the short answer is that the plate voltage should swing both ways
from the operating voltage if real music is applied; perhaps all that
is wrong in your simulation is the sign of an input... Generally
speaking, unless you really know what you're doing, simlations are
pretty
much useless to teach yourself anything, unless you write the sim
yourself and thus in the process force yourself to understand the
interrelationships; I used to write mine in the spreadsheet MS Excel
and still use it to draw me a quick graph to see how flat any new amp
or stage will be.

A far more useful tool, if you're just starting out in tubes, is
working on your computer or on printed paper with the transfer curves.
They hold a very rich store of information. When you have understood
what happens inside the tube will be ample time to put it in a network
and take the characteristics of the output into account.

Download this illustration from my netsite
http://members.lycos.co.uk/fiultra/112KISScurves.jpg
and find the point Q defined by Ebq and Ia. That is the design centre
operating point. The drawing shows that on the application of signal
the plate voltage swings. In which direction the voltage swings depends
on whether the signal is positive or negative going. That is shown by
the superimposition of blue and red lines on the seagreen loadline (the
5K6 of my chosen transformer primary passing through the quiescent
operating point marked Q).

The process of arriving at this wealth of visual information is
described at my KISS Amp netsite
http://members.lycos.co.uk/fiultra/The%20KISS%20Amp%20INDEX.htm
in the chapter "Choosing an operating point for a new design"
http://members.lycos.co.uk/fiultra/KISS%20112%20by%20Andre%20Jute.htm

You may want to read some of the other chapters thereabouts which go
into more depth about calculating distortion off the same graph, and so
on.

HTH you find to become Found.

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

[Ian Iveson]

Lost'n Found wrote

> I am using PSPICE to simulate the output stage of a tube amplifier.
> I am using a 420v DC and an output transformer.
>
> The voltage on the plate of the tube swings between 840v and 420v. I
> know that the output transformer opposses the current change, but I
> thought that the voltage should swing up and below the 420v, not
> between 840v and 420v.
>
> Is it operating correctly? I mean can the voltage swing between VDC
> Max and higher?
>
> thank you for your time.
>

Voltage across an inductor is proportional to the rate of change of
current through it. You should be able to observe that clearly.

Transformers are not native to spice, AFAIK, so much depends on your
model. It should behave like the primary inductance in parallel with
the reflected secondary load (ie the secondary load multiplied by the
square of the winding ratio). If the model includes leakage and
primary capacitance, they will modify the behaviour at higher
frequencies, as if the capacitance was in parallel, and the leakage in
series, with the primary inductance.

But why doesn't your voltage drop below 420V?

cheers, Ian

[Peter Wieck]

Andrew Jute McCoy invaded a thread where it has nothing to add:

>To sound as if it actually knew something about Spice...

It does not.

Peter Wieck
Wyncote, PA

[Ian Iveson]

Patrick Turner blethered

> Trying to get any simulation program to correctly simulate the much
> varied
> distortion
> spectra of an output pentode with loads between 1k and 10k would be
> rather
> difficult.

How would you know? You don't even know what SPICE *is*.

> I never simulate very much because its being bone lazy.

Because you can't. Because you are too idle to learn how. Because you
don't design anything anyway. You just copy circuits and then lie
about them.

> I go to my workshop
> and build the test circuit. I deal with REALITY BEHAVIOURS.

You poorly solder together copied circuit, fail to test it thoroughly,
tell a heap of lies about it, and sell it to someone with more money
than sense. That's your "reality behaviour".

cheers, Ian

[Chris Hornbeck]

On Sat, 16 Sep 2006 08:01:40 GMT, Patrick Turner
> wrote:

>This release of stored magnetic energy in the inductance of the choke or OPT is a
>mysterious business.
>Why does the signal usually closely follow the tube's commands when it rises
>above the anode DC supply?
>
>What happens if the flow of dc in the L is interupted in an extremely short time?
>
>what stops the stored magnetic energy from producing a voltage rise that is
>infinite?

And, before anybody gets too pedantic, Yes, Patrick *does*
understand these issues.

The questions are raised in a way to encourage thought in
the reader. Hopefully not totally lost on the readership.

All good fortune,

Chris Hornbeck
"We can teach computers to lie to us however we choose. Lying to
ourselves takes much more talent and suffers many more failures."
-Al

[Eeyore]

> On Sat, 16 Sep 2006 08:01:40 GMT, Patrick Turner wrote:
>
> >This release of stored magnetic energy in the inductance of the choke or OPT is a
> >mysterious business.

No it's not.

Graham

[Patrick Turner]

Ian Iveson wrote:

> Patrick Turner blethered
>
> > Trying to get any simulation program to correctly simulate the much
> > varied
> > distortion
> > spectra of an output pentode with loads between 1k and 10k would be
> > rather
> > difficult.
>
> How would you know? You don't even know what SPICE *is*.
>
> > I never simulate very much because its being bone lazy.
>
> Because you can't. Because you are too idle to learn how. Because you
> don't design anything anyway. You just copy circuits and then lie
> about them.
>
> > I go to my workshop
> > and build the test circuit. I deal with REALITY BEHAVIOURS.
>
> You poorly solder together copied circuit, fail to test it thoroughly,
> tell a heap of lies about it, and sell it to someone with more money
> than sense. That's your "reality behaviour".
>
> cheers, Ian

Ian Iveson helps to make rec.audio.tubes into an intellectual sewer.
He's built one amp after 5 years, and declares himself an expert.

Ian is not a profific maker of anything except BS.


If I needed to simulate something the way the army of ARMCHAIR SOLDERERS
do, I would,
but I am too busy making real gear for sale.

Patrick Turner.

>
>