LTspice tutorial - Modeling vacuum tube triodes

#97 #ltspice
In this video I continue looking at how vacuum tubes are modeled - in particular I look at the triode. I cover the basic mathematical models available, and I implement one of the in LTspice. Then I try to extract the characteristic parameters for a random vacuum tube, and finally try out the model in comparison to a real life circuit.

Model and spreadsheet:

Research papers:
Datasheets:

LTspice Tutorial series:
EP1-Getting started:
EP2-AC simulation and the Baxandall tone control circuit:
EP7- Dependent voltage and current sources
Ep8- Turning a datasheet into a component model
EP9- Independent voltage and current sources
Ep10- .wave statement and audio file processing
Ep11 The effect of temperature on your circuit
EP12 Modeling a DC brushed motor
Ep13- Worst Case, Monte Carlo and Gaussian statistics circuit analysis
EP15- SMPS EMI and electrical noise and filters
EP16- Feedback loop simulation
Ep17 - Verifying Simulation Models
Ep18 - Simulating Capacitors
Ep 19 - Simulating Inductors
EP 20 - Noise simulations
Ep21 - Models and Libraries
Ep22- Voltage and current limited source
Ep23- Measuring Power Factor
Ep24 - Modeling a vacuum tube triode
Ep25- Using standard symbols

Special Thanks to all my supporters on Patreon! Especially @afiskon and Xegomen!

If you liked this video be sure to check out my other videos and you can also subscribe to be up to date with all the new ones!

[brandonavo]

This video is absolutely incredible and a huge resource. Thanks for explaining the circuits in the paper and how they match up to LTspice in a clear manner. Triode stuff is hard to find these days especially explained in such a nice way. Subscribed.

[keithgreiner]

This is an amazing presentation and is just exactly what I am looking for. I’ve been studying it.
I have a few questions. First, I am trying to replicate the example LTspice models. I am not getting the same results as shown on the screen. I think there are several issues. First, when I stop the presentation and try to read the characters on the screen, some are fuzzy and difficult to get right. Would it be possible to post high-definition images of the screens so I can be sure of the values I am typing in? Second, after I do get the programs running, I am not getting the same graphs. With the .tran 1 statement, all I get for anode voltage and current is a straight line. So I am making a mistake but I don’t know what it is. It may be that I have some incorrect statements. But it also might be that I’m not following the exact steps used to create the graphs (ie: the graph at 4:23). Can you please explain the specific steps used to create the graphs? Where did you place the cursor? Did you select voltage or current at that location? Third, in LTspice, I am not finding an StR85/10 tube. Is there a substitution that would be in LTspice? Is there a Zener diode that woujld work in this instance and still return similar results? Thank you very much.

[adrianrevill]

Thanks for the video, I worked through how this modelling worked a few months ago and then put the project aside. This was a perfect refresher.

[NicoV-ybgf]

Thank you sir. You saved me A LOT of time here. I just wanted models so I can predict approximate voltage and current levels. I used "multisim" to test their model of a 12ax7 in a JCM800 pre-amp circuit. I got 668 Vp-p on the last gain stage anode/CF grid, while only using 300V B+!! I knew something was off. Probably using that model that doesn't cater for positive grid voltages, giving me -400v odd swing below ground!!
Now I will try ltspice with your model. Hopefully I will get to more accurate signal voltage levels.

[astorina]

Thank you for sharing your knowledge and prospections
Take care

[yveslesage]

Just a single word... Brilliant ! Thanks Mr Fesz

[p_mouse]

Absolutely excellent video!
In fact I was just about to model a few myself, but most tutorials are just not very clear imo. Thanks for clarifying a few thing! And yes that overlay trick works great, I use it all the time! 😎👍🏻👍🏻👍🏻

[thevicol]

Excellent explanation. But when we get into the details a few aspects are worth noting. 2:59 The diode and resistor is a bit oversimplified model of the grid current. It does not take into account the influence of the anode voltage. The improved Norman Koren' s model does a good job of representing the triode stage's behaviour in what we would call 'the more linear regions of operation'. It also takes into account the influence of the tube socket and leads capacitances on the frequency characteristics. But if we are interested in analysing non-linearities in terms of the distortion characteristics, it is worth to use a model created by Ayumi Nakabayashi. At least when it comes to triodes in pre-amp circuits. Power amplifiers are a separate story and here all accuracy limitations of tetrode and pentode models come out quite noticeably. There is quite an extensive discussion about tube simulation on the diyaudio forum. There were also quite interesting attempts to improve the precision of mathematical representations.
It is also interesting, that on some schematics the given filament voltage is slightly lower than recommended in the datasheets. These are not big differences, but they can affect the operation of some stages. The only model that takes into account the effect of heating is the one created by Duncan Munro, although the precision of this model is not better than that of N.K. or A.N. models.

[bcsongor]

"Tubes are not efficient, but they are pretty.".. also they sound pretty good in amps :)

[AndrewCaldarone]

How do you add the custom diode model to the diode on the schematic? I can't type in the "Diode" box so I can't change "D" to "DGK"

[sim_]

Thank you!! Really great tutorial, thank you very much.
So, can i replace the Ia/Va graphic with others of different tubes datasheets and try to find parameters for them(using your spreadsheet)?

[francescodilorenzo]

Very nice video, I'd like to know if you can give me some adevice to simulate a circuit with 4cx250, or I can use an equivalent vacuum tube, becasue I'm not an expert of Vacuum tube. Thanks

[zd]

nice trick overlapping the plot from the datasheet with the one made in excel

[francescocanora]

bravo! Is possible tutorial for pentode ? thanks

[KamleshGadhvana]

nice one please do simulation on audio equalizers with circuit

[andreybrodianski]

Hi. I had very accurate working model of vacuum tube 12AX7. After refreshing my PC new installation (with new blue buttons tool bar) doesn’t run old saved files with tubes. Do you know what is the issue?

[sanjikaneki]

how do you determine slew rate of a op amp in LTSpice?

[debunker]

It is not convenient to adjust the coefficients in the Excel file. There is a simple and convenient program for creating spice models java jar file paint_kit.jar. Why do what has already been done?