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In message <j55k6t+5cer@...>, dated Sun, 18 Sep 2011, Charly Engineering <charly020664@...> writes:

I don't understand why the EC86-transient-analyse is succesful and the EC81 with the Koren_Tube-model in nearly the same circuit not.

Maybe the models differ in some vital respect. Please upload your EC86 .asc and model.
--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
When I point to a star, please look at the star, not my finger. The star will
be more interesting.

It would help if you told us what you are trying to make a simulation
of.
--

Yes, I work at noise-matched active antennas. The Rser and Cser of the voltage-source simulate a electrical short antenna at about 1 MHz.

I would not try to use a tube, but unfortunately I need big signal solidity up to fields of 20 V/m or 30 V/m for usage near a big transmitter.

I try to aspire a bandwidth from 10 kHz to min. 30 Mhz. 10 kHz is not simple with a tube.

I first tried with an EC86, that works, but an EC81 is much more better like my databook told me.

It is the first time, I used a Koren_tube model from the lib. For the EC86 I used another model.

Don't think about the 1 mH-transformer, it's only for testing here.

I don't understand why the EC86-transient-analyse is succesful and the EC81 with the Koren_Tube-model in nearly the same circuit not.

thanx, best regards, Leo

In message <j55dke+dhss@...>, dated Sun, 18 Sep 2011, Charly Engineering <charly020664@...> writes:

I asked here for a model for the EC81, Suusi Malcom-Brown-B was so kindly to add the model to the Koren_tubes.cir-lib.-

Now I have the problem that a transient analyse delivers curious results.-

Everything delivers curious results. You have just a 1 mV input signal, which at low frequencies is attenuated further by the 18 pF capacitor and the 1 meg resistor, and the EC81's input capacitance.

Then you ac sweep goes to 500 MHz, at which frequency the 1 mH anode load has an enormous impedance and is quite impracticable.

I'm not very experienced with tubes, so I've uploaded the EC81-test-files to the folder temp.

It would help if you told us what you are trying to make a simulation of.
--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
When I point to a star, please look at the star, not my finger. The star will
be more interesting.

Hi
i'm looking at an impedance curve of a non-ideal tantalum capacitor in LTSpice. The test circuit and impedance curve is seen in this screengrab:

The spice file is here .
So, the imdpedance curve shows the expected impedance minimum, but also an unexpected maximum at about 100MHz, where there is also a polarity switch in phase. This feature does not show up if I do an impedance plot in octave:


octave:1> f = [1000:1000:1e9];
octave:2> C = 2e-3C = 0.0020000
octave:3> R = 2e-3R = 0.0020000
octave:4> L = 1e-9L = 1.0000e-09
octave:5> z = R + f.*2*pi*j*L-1./(f.*2*pi*j*C)
octave:6> loglog(f,abs(z))
octave:7> semilogx(f,atand(imag(z)./real(z)))

Which result in these plots



The parameters in the octave code are the same as in LTSpice component. Anyone know where this comes from? The phases look pretty different, is there something wrong with the test circuit?

Hi,

I asked here for a model for the EC81, Suusi Malcom-Brown-B was so kindly to add the model to the Koren_tubes.cir-lib.-

Now I have the problem that a transient analyse delivers curious results.-

I'm not very experienced with tubes, so I've uploaded the EC81-test-files to the folder temp.

Perhaps s.o. can look, that would be great.

pre-thanx, best regards Leo

In message <4E762028.8050305@...>, dated Sun, 18 Sep 2011, Ganesan <dg1@...> writes:

My personal experience is de-rating the heaters to about 90% and putting a mini fan.. can double or triple the life of these old valve baseed equipment..

I agree with the fan, but I don't see how you can show double or triple life, unless you are basing it on 1970s poor-quality products (mainly bad vacuum and bad welding). Well-made valve/tubes typically last 10 years, so to show triple life you would have to run tests for 50 years.

I have some 50 year old test equipment that still works within spec with the valves that were in there when I bought the gear in 1984.
--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
When I point to a star, please look at the star, not my finger. The star will
be more interesting.

In message <1316365434.4717.56.camel@Yoda>, dated Sun, 18 Sep 2011, Peter <pmoss@...> writes:

Why is LINUX not a threat to windows?

There is no truth in the rumour that the release name of "Windows 8" will be 'Eyelynucks'.(;-)
--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
When I point to a star, please look at the star, not my finger. The star will
be more interesting.

On Sun, 2011-09-18 at 12:11 +0000, LTspice@... wrote:

Re: What changes would make LTspice better?
Posted by: "martin562284"
martin.sadler@... martin562284
Date: Sun Sep 18, 2011 12:07 am ((PDT))

Peter,

your opinion is as valid as any one else's - I don't agree with you,
but that doesn't mean I'm right and you're wrong, or vice versa.

As far a Linux is concerned, we've obviously had quite different
experiences. Clearly, this is OT as far as this group is concerned but
if you want to discuss further let's do it via private e-mail.

Nope, I did not expect many to agree ;-) They are not new users ;-)

But the point is a problem/suggestion was highlighted and quite
correctly so. The solution must also be a solution that addresses the
problem because the problem exists and will continue to as long as it is
not addressed. Is there any point in trying to fine tune the ECU when
the wheels are falling off?

It is quite obvious and possibly understandable the annoyance and
intolerance many have of repeated beginner questions. That is a very
very obvious and simple indicator that the place to begin is to address
the most common problems and difficulties beginners have. Not to try to
circumvent addressing the problem.

Goodness, windows users have difficulty with the F1 key but it is there.
LTspice does not have to be the leading "ease of use" program and I am
not suggesting that it should be but there are areas that could do with
a lot of consideration.

LTspice is a great program of that there is no doubt. Can it be better,
you bet. Will it be better if it panders and accommodates only the
"demands" of expert and experienced users or the general run of the mill
user and new user? Who is likely to appreciate any improvement the
most? Who gets to reap the benefits of the time, money and effort?

Consider what a relief it would be to have those annoying questions
diminish by a significant figure. Consider that they are the base of
the pyramid, the source of most frustration and reason many will find to
give up on LTspice and find something easier more intuitive to use. Do
they even care about the technical excellence?

Google windows ~8 Billion
linux 838,000,000
free ~15 Billion
ltspice 526,000
pspice 2,590,000

When the answer is known maybe that will make what I said a lot
clearer.

I use LINUX on this PC, I'll boot to windows occasionally because wine
and LTspice is chronically crippled by the LINUX VIA openchrome drivers
which have to be manually installed and setup. I am dinosaur. ;-)

LINUX is no longer an insignificant operating system but it is no real
threat to Windows or M$ would be making bids. Why is LINUX not a threat
to windows? In many aspects it is technically superior..... It does
not require user training, more manuals, more tutorials, better help,
tinkering with the engine.... There is a lesson in that somewhere.

A twitter user probably knows how to say this better. I don't ;-)

Thanks Martin for the response and offer but I think all has been
said ;-) I'm not trying to ride a hobby horse and it really is up to
LT. I have no idea of what LT expects or wants from LTspice and that is
vital to know in order to answer this question.

I have also been away so apologise if I missed other responses.

--
Regards
Peter

--- In LTspice@..., Ganesan <dg1@...> wrote:

My personal experience is de-rating the heaters to about 90% and

That's interesting - I've never come across anyone who's actually tried that until now - so maybe the old wise one's are not so wise, after all! I must say that I've been working with valves for only about 7 years now and I haven't had problems with any valves in my designs coming to their end of life yet - although they don't get used an awful lot, either.

I have a few items of vintage gear that are still running fine, although I haven't checked to see if the valves are still running to spec.

putting a mini fan.. can double or triple the life of these old valve
baseed equipment.. Putting a series resistor with the heater puts out
the same amount of heat in the system...

Yep, I've used mini-fans in a couple of my designs, too. They certainly keep things cool, which can only be good - not just for the valves.

But I will defer to your
expertise...

Definitely not an expert, just a fellow seeker of knowledge and enlightenment!

Martin

In message <j555at+95dr@...>, dated Sun, 18 Sep 2011, Tony Casey <tony@...> writes:

Confucius say: Things remain hidden mostly for want of looking. :-)

Looking for an analoguespiceman award?(;-) The problem is not looking, it's guessing where to look, on the understanding that the needle may not be in the haystack at all, and it may be a thorn rather than a needle.
--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
When I point to a star, please look at the star, not my finger. The star will
be more interesting.

My personal experience is de-rating the heaters to about 90% and
putting a mini fan.. can double or triple the life of these old valve
baseed equipment.. Putting a series resistor with the heater puts out
the same amount of heat in the system... But I will defer to your
expertise...
Cheers
AG

--- In LTspice@..., Ganesan <dg1@...> wrote:

My question is, Whether the plate current to heater coupling is
correctly modeled through an rms function ?
Cheers
AG

AG,

non of the valve (tube) models I've come across (and I've seen quite a few) model the effect of varying heater current or voltage - they simply (attempt) to model the relationship between the electrode voltages and currents. In effect they assume that the heater is working at nominal voltage/current from time zero. If I need to modal the heater current draw when working on power supply designs I usually just use a resistor or current sink.

If you are interested in the heater transient behaviour at switch on/off, the guy who runs the DuncanAmps site (www.duncanamps.com) has done some work on this, I believe. You could also take a look at our own Helmut's and analog spiceman's excellent work on filament lamps in the Files section of this group.

Please note that running heaters at anything other than nominal voltage current is not recommended. Over OR under can shorten their life.

Do be aware that most, if not all, of the models are reasonably accurate only over a limited range. Operation outside of or even near the extremes of the characteristic curves published on the datasheets should not necessarily be considered as real-world behaviour.

Martin

--- In LTspice@..., "Suusi M-B" <smalcolmbrown@...> wrote:

I have added EC81 and 6R4 to the Koren_Tubes.cir library see the message
49829


Suusi Malcolm-Brown

WOW, You are sooooooo good to me :-), thanx ....

best regards Leo ...

OK Helmut,
many thanks

--- In LTspice@..., John Woodgate <jmw@...> wrote:

In message <j54t57+aisu@...>, dated Sun, 18 Sep 2011, Tony Casey
<tony@...> writes:

I've uploaded to File>Temp a screenshot of what you need to change to
banish your greys.

Thank you. Yet another hidden wonder!
--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
When I point to a star, please look at the star, not my finger. The star will
be more interesting.

Confucius say: Things remain hidden mostly for want of looking. :-)

In message <j54t57+aisu@...>, dated Sun, 18 Sep 2011, Tony Casey <tony@...> writes:

I've uploaded to File>Temp a screenshot of what you need to change to banish your greys.

Thank you. Yet another hidden wonder!
--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
When I point to a star, please look at the star, not my finger. The star will
be more interesting.

In message <4E75F5EB.8040605@...>, dated Sun, 18 Sep 2011, Ganesan <dg1@...> writes:

Thanks.. i think some tubes used to carry plate current curves for different heater powers.. If going to 5.55 volts instead of 6.3 doubles
the tube life, very few wouldn't do it..

The loss, and increased variability between samples, of performance is quite significant, and longer life is not assured, because 'cathode poisoning' (contamination by outgassed contaminants) is more of a problem at lower cathode temperatures.

The best way of lengthening life is 'keep it cool and limit the switch-on surge in heater current'.
--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
When I point to a star, please look at the star, not my finger. The star will
be more interesting.

In message <[email protected]>, dated Sun, 18 Sep 2011, Suusi M-B <smalcolmbrown@...> writes:

In the real world there is quite a difference between individual valves of the same type

They are a sort of FET, after all! (;-)
--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
When I point to a star, please look at the star, not my finger. The star will
be more interesting.

Kudos Tony,

Your response is extremely well written - clear and lucid,
employing a keen understanding of the minutiae of LTspice to
thoroughly answer Landrum's somewhat veiled request. Bravo for
for correctly using the b-source time step control parameters,
tripdv and tripdt - most people miss that. -- a.s.

PS: Got your email regarding the improvement of Help. I am going
to be incommunicado for a few days, but anyway I wanted to wait
to see what response Lewis gets from Mike regarding permission
to copy the existing Help to the LTwiki as a foundation upon
which to build our own expanded Help colossus. :)

--- In LTspice@..., Tony Casey wrote:

--- In LTspice@..., Landrum Haddix wrote:

I've been measuring lots of ripple voltages on DC power supply
voltages. Is there a way to get a waveform showing RMS AC volts
regardless of offset.

You questions are somewhat ambiguous, since there is no such
thing in this context as an RMS AC waveform.

If you just want to look at the AC portion of the waveform in
the viewer, you have several choices:

- Change the Y-axis plot range to only show the portion of the
waveform, you're interested in. This method has the disadvantage
that every time the viewer re-plots, it will autoscale so you
will have to repeat the scaling exercise. An alternative is to
save a .plt file with your preferred axis settings, and reload it
each time the waveform is re-plotted. Hint: assign a Hotkey to do
this. I use [spacebar] like others have mentioned recently.

- Plot the quantity V(ACnodename)-DCOffset (where DCOffset is
the numerical value for the estimated offset.

Of necessity, this will be a manual process, as the waveform
viewer has no way of knowing what you mean it to plot.

When the occasional need for this operation arises, my method
is to zoom in on either an integral number of cycles or a large
number of non-aligned cycles and ctrl-left-button click on the
trace label to read the average value of the trace. I then edit
the waveform expression to subtract this exact amount.

Alternatively, you can carry on doing it your way, but with the
same advantages and disadvantages as AC-coupling with a real
scope.

If you actually want to measure the rms value, as suggested by
the title of your post, you can use post-processing scripts to
calculate that from the simulation data.

Add the following lines in a SPICE directive:
.meas TRAN Vavg avg V(out); calculates the DC offset
.meas TRAN Vrms rms (Vavg-V(out)); calculates rms after
substracting the average

You will find the results of these calculations in the logfile
after each simulation. Of course having found the average value
by this means, you can then substitute its value into your viewer
plot expression. This is helpful since if you are also performing
a .stepped simulation, the Waveform Viewer won't calculate the
average and rms values of a waveform.

One more tip: if the AC voltage is small compared to the DC
offset, you will also need to add the directive:
.option plotwinsize=0

...too, or the waveform compression will distort the ripple
voltage and the rms calculation will be wrong.

There's also a really nerdy way to display exactly what you want
to see in the waveform viewer, but it requires some subterfuge,
and can only show the ripple voltage right at the end of your
tran time, since it calculates the DC offset on the fly. This
will only work if your DC offset is stable over time. You can
find this example as RMS_Value.zip in Files>Temp

<snip>

Yes, that's what I meant. Time to upload, clearly. See the zip archive
Pos and neg doubler rectifiers.zip It looks better if you 'Tile
vertically', which the .plt file apparently doesn't save.
--

</snip>
Hello John,

I've uploaded to File>Temp a screenshot of what you need to change to banish your greys.

Regards,
Tony