The paper explaining the theory behind the model has been accepted for publication at ISCAS 2009 (International Symposium on Circuits and Systems), to be held in Taipei, Taiwan on 24-27 May 2009
22 March 2008----ADDED SVETLANA SV572-3 Pspice Model--Download at the bottom of the page!!!
Hi guys,
my name is Leonardo Di Carlo.
This is my new Vacuum Tube page and it will be update as soon as possible.
I've developed a new 12AX7A Pspice Model and other interesting things I will post in the next future.
Unfortunately I have not much time in this period and so I can't explain u the theory behind my little work in detail but i will do it
after my graduation.
I'm very interested on your comments,critics and so on.
This model could be improved if I know reliable data of input
grid current and\or plate current at positive grid voltage.So if anyone tested these on the bench i will appreciate
to receive these data.
I hope my work could be useful for you.
PSPICE MODEL 12AX7A "Dream" Model (brief explanation)
U have to consider these models as beta versions but i've yet tested them on an complete amplifier
and it works properly and if u have some problem I could give u some suggestion to solve them.If u take a look to the model it could
be seem crazy.The only thing i can say to u now is that is based on interpolation,but I'm working on a "slim" model
with less intepolation effort and more analytic relationships.I think it will be ready in the next months.
The main drawback of this one is that it's time consuming and it needs a powerful processor.The bigger the circuit the slower
the simulation.I've checked that simulating a whole amplifier it's about 20 time slower than popular Koren Model (with a 1.66Ghz Dual Core Processor).But now u have an active grid circuit with a grid current that is function of Vgk and Vpk
Unfortunately I need more information about grid current I couldn't find anywhere and so i will appreciate your support.
That's why i posted a model labeled as passive because i left the Leach\Koren input circuit with it's strange things (negative diode
saturation current,Vpk independence and so on...)if u have some problem with the active one try the second until i
set the input current properly(it's crucial in evaluating distortion!).
Some hints:
- Be sure that the first time ABSTOL is set at least at 1pA or smaller,RELTOL=1e-3 or smaller,ITL4 =40
- If u try a big simulation switch the data collection option to "all but internal subcircuits" otherwise u will receive "Disk Write error"
- During a DC sweep u could see some strange curves but they are very far from load lines points.
- The model is reliable until 1.5 positive grid voltage.I calculated the curves from theorical consideration but
i can extend the range if i have more data.
A New Approach (update August the 29th 2007)
I have developed the second version of my "Dream" 12AX7A Pspice model.It's based on a new approach that mixes interpolation and analytical relationships.
I will explain it in detail later as i said before.This model is reliable also in higher power dissipation zones.But the most important thing
is that also the grid current is modeled.You always have to consider this a beta version also because i developed it in few time and i can model grid current also better
but i'm not sure that such a precision is so important.In order to do that I used the data sent to me by Robert McLean and so I want to express my gratitude to him.
His data are a little bit different from RCA datasheet for some values of grid voltage and so I tried to find a balance between them.That's why i think that some
improvement could be done with some more averaged data.But i think that this approach is good and it can also be applied to pentodes.As the previous one, this model is reliable until +1.5 grid voltage.
VERSION 2.1
Major features
• Transition through curves smoother (gm more reliable)
• size of the code much much smaller
Notes:
There is a still some uncertainty about K1,D1,Voff.U can try to vary the values a little bit.
Static characteristics are almost the same as V2.0.Only curves in positive grid voltage are slightly "higher" and so saturate slowly.
VERSION 3.0
(update January the 20th 2008):
Here we are with the 3rd version of my model. This one contains a lot of improvements
1) The variation of parameters has much more physical meaning.
2) "Tube constants" match datasheet data. I added the approximate numerical evaluation plot of gm
3) I added a saturation law for the "current limited by temperature" zone. I used the same idea developed for a triode model
model by EXCEM in '93. I found very strange that no one mentions this model that ,in my opinion, is the best found until now.
Maybe because there are a lot of parameters that the user doesn't know. I used a random value for "Isat" just to show the effect.
The nominal value comes from Richardson law and u have to know the work function of the oxide-coated cathode and
it's temperature.
4) The model is very "light" and now it's simulation speed is equal or even faster than the Koren Model.
On the next month i will come with the complete explanation of the idea's behind the model.
Download this files:
» Dream_v20.txt
» Dream_active.lib
» Dream_passive.lib
Keep on Tube Rockin'!
my email:
