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Problems with Multisim tube models
Problems with Multisim tube models
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Old 4th November 2017, 06:51 AM   #11
jazbo8 is offline jazbo8
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Problems with Multisim tube models
URAMP is one of the basic functions of SPICE since day one, any program that can not handle it well should be tossed in the bin... As to your question - for triodes, all of the model types work fine - unless there is grid current, then Ayumi is preferred. For pentodes, I only use the Ayumi models unless the Reefman models are available.
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Old 4th November 2017, 10:03 AM   #12
flex2 is offline flex2  Sweden
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Quote:
Originally Posted by jazbo8 View Post
URAMP is one of the basic functions of SPICE since day one, any program that can not handle it well should be tossed in the bin... As to your question - for triodes, all of the model types work fine - unless there is grid current, then Ayumi is preferred. For pentodes, I only use the Ayumi models unless the Reefman models are available.


Send my fine Multisim to the bin?
Naah...

Thank you very much for your thoughts about which models to go for.
Very much appreciated...

Have attached a picture where I test three different tubes and type of models.
The generic delivered with Multisim do not handle 2nd harmonic correctly so that's why I try to find better models.

Both Ayumi and the 8 parameter Norman Koren (modified by Wayne Clay) get the 2nd harmonic according what I expect it to be.

But there are approx. 10dB difference between them regarding the 3rd harmonic.

Any comments on that?

Which model du you think gets closest to a real world circuit?

VCC = 150 Volt
Anode resistor 16K
Cathode resistor 470
Grid series resistor 1K
Input 1.0 Volt at 10 kHz

Edit:
Sorry, got the wrong color on the generic 6922 in the oscilloscope where it is blue, hard so see, but in the middle of the green and red curves.
Attached Images
File Type: jpg Distortion.JPG (346.8 KB, 65 views)

Last edited by flex2; 4th November 2017 at 10:08 AM.
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Old 4th November 2017, 10:38 AM   #13
jazbo8 is offline jazbo8
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Problems with Multisim tube models
Given the tubes' tolerences, no one knows for sure... The SPICE models can only give you a good idea what to expect, but only a breadboard with actual tubes can give you the exact distortion figures when they are measured on the bench.
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Old 8th November 2017, 12:09 PM   #14
jackinnj is offline jackinnj  United States
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Problems with Multisim tube models
Quote:
Originally Posted by flex2 View Post
Just spent a day to read through this thread and I very much appreciate your efforts and sharing of information.

I use NI Multisim 13 at the moment and found a couple of comments that Ayumi's models don't work very well in that software.

Is that a true statement?

Are there any other library of models that work better for Multisim or do I need to go over to LTSpice or some other software to be able to simulate for proper results?

There have been a lot to take in, so I'm a little bit confused at the moment, so any help to get me in the right direction would be helpful.
For some reason, Multisim isn't happy with so many "behavioral" directives. Some of the syntax is a bit different, but can usually be corrected with little difficulty.

For triodes the Koren models work well. If you are using an tube without a model, it isn't difficult to find the parameters using Microsoft Excel's "Solver" function.

Robert Weaver posted (and corrected) a method for solving pentodes. Pretty complex but well thought out: Vacuum Tube SPICE Models
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Old 8th November 2017, 06:09 PM   #15
flex2 is offline flex2  Sweden
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Quote:
Originally Posted by jackinnj View Post
For some reason, Multisim isn't happy with so many "behavioral" directives. Some of the syntax is a bit different, but can usually be corrected with little difficulty.

For triodes the Koren models work well. If you are using an tube without a model, it isn't difficult to find the parameters using Microsoft Excel's "Solver" function.

Robert Weaver posted (and corrected) a method for solving pentodes. Pretty complex but well thought out: Vacuum Tube SPICE Models
Seems like time step locks into very small steps despite what your set.
Just as you say, I too have found Koren's modell to work fairly well and gives much more "real" results compared to the Generic types included in Multisim. But occasionally it too runs into problems if the circuit have long settling time because it will not run unless it "Start from Zero".
It's a pity because I really like Multisim otherwise.
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Old 9th November 2017, 01:09 PM   #16
jackinnj is offline jackinnj  United States
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Problems with Multisim tube models
Quote:
Originally Posted by jazbo8 View Post
Very few people use Multisim here, so to use the Ayumi or the other models shown in this thread, you will need to do a bit of translation on your own, but it should not be difficult.
Just a historical reference -- back when we were using '286s the antecedent of Multisim was almost given away -- something like $70. Then National Instruments bought the company and drove the price up 20x.

NATI did the same thing with "Softwire" -- a program which could have upended their T&M business -- Softwire was free-ware distributed with ADC/DACs -- to write the code you just attached "wires" in a graphical setting. NATI bought Softwire and stopped selling the stuff.
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