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5th July 2005, 09:51 AM  #1 
diyAudio Member
Join Date: Jul 2005
Location: Hilleroed, Denmark

CircuitMaker Vacuum Tube model
Can anyone explain the vacuum tube model parameters in CircuitMaker 2000. Below the original 12AU7 model.
*Vacuum Tube Triode (Audio freq.) pkg:VT9 (A:1,2,3)(B:6,7,8) .SUBCKT X12AU7 1 3 4 B1 2 4 I=((URAMP((V(2,4)/18)+V(3,4)))^1.5)/1151 C1 3 4 1.6E12 C2 3 1 1.5E12 C3 1 4 0.5E12 R1 3 5 10E+3 D1 1 2 DX D2 4 2 DX2 D3 5 4 DX .MODEL DX D(IS=1.0E12 RS=1.0) .MODEL DX2 D(IS=1.0E9 RS=1.0) .ENDS X12AU7 I think that I have found some of the parameters: ?=Don't know *Vacuum Tube Triode (Audio freq.) pkg:VT9 (A:1,2,3)(B:6,7,8) .SUBCKT X12AU7 1 3 4 B1 2 4 I=((URAMP((V(2,4)/18=my)+V(3,4)))^1.5=?)/1151=? C1 3 4 1.6E12 = Grid cap. C2 3 1 1.5E12 = GridPlate cap. C3 1 4 0.5E12 = Plate cap. R1 3 5 10E+3 = Ri D1 1 2 DX = ? D2 4 2 DX2 = ? D3 5 4 DX = ? .MODEL DX D(IS=1.0E12 RS=1.0) = ? .MODEL DX2 D(IS=1.0E9 RS=1.0) = ? .ENDS X12AU7 
5th July 2005, 01:59 PM  #2 
diyAudio Member
Join Date: May 2005
Location: Stittsville, Ontario, Canada

Steen
mu is approximately 18 exact values of mu, gm and rp can be calculated, but I will have to get back to you on that 1151 sets the overall emission ^1.5 is the exponent, ie sets the rate of curvature of each grid curve R1 is not rp. R1 is there to set grid current for 1ve grid voltage, which is modeled by a resistor and diode in series. D1 is a diode to make sure current only flows from plate to cathode. I am not sure why D2 is used.
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Robert McLean 
5th July 2005, 02:16 PM  #3 
diyAudio Member
Join Date: May 2005
Location: Stittsville, Ontario, Canada

Actually, I must correct myself. After doing the math I see that for this model mu is exactly 18 for all voltages.
gm is given by 1.5 * sqrt( Vp/18 + Vg) / 1151, and rp is given by 1151 * 18 / ( 1.5 * sqrt( Vp / 18 + Vg )) mu = gm * rp The constant mu is an indication of the simplicity of the model, but it is quite useful anyway.
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Robert McLean 
5th July 2005, 02:37 PM  #4 
diyAudio Member
Join Date: Nov 2003
Location: Genova, Italy

d3 with R1 (badly) models grid current
Federico 
6th July 2005, 06:29 AM  #5 
diyAudio Member
Join Date: Jul 2005
Location: Hilleroed, Denmark

Hello Robert
Thank's for your qiuck answer and explanation of the parameters of the model. Now the values makes sense, so I can add new models. I planning to add the 12AT7 and 6922 tube. I know it's a simple model, but i works ok. I have used CircuitMaker's buildin models and the simulation results are ok and within what you can exspect. Steen 
6th July 2005, 07:22 AM  #6  
diyAudio Member
Join Date: Nov 2003
Location: Genova, Italy

Hi Steen
Quote:
Child's law, in fact, describes in a satisfactory way the real behavior of a triode only in case of great currents values and small potential differences Vak. the posted figure shows the behavior of a real world triode in comparison to the model of Child, the fitting has been obtained imposing minimum error in case of Vgk=0 and 2. Curves obtained with Child’s law for different values of Vgk are simply translation of the one for Vgk=0. In real curves instead, current fixed, the slope of the curves decreases as Vak increases and we see a remarkable departure of the model from the real behavior. Use Koren model for a better fitting bye Federico curves from http://www.audiomatica.com/tubes/6sn7.htm 

6th July 2005, 07:23 AM  #7 
diyAudio Member
Join Date: Feb 2005
Location: Zagreb

They will be fine for operating point analysis, unless you are using very low currents (for a given tube), or want to analyse distortion, in which case you will get wildly optimistic results (as in 10x better than reality).

6th July 2005, 09:33 AM  #8 
diyAudio Member
Join Date: Jul 2005
Location: Hilleroed, Denmark

Hi
Thank's again. I won't use the CircuitMaker for any optimation and distortion analysis, only for schematic capture and some first hand operating point settings. I belive that if serious analysis is the quest, then PSpice is the answer. P.S.: I'm new to Spice simulation. Steen 
6th July 2005, 11:25 PM  #9 
diyAudio Member
Join Date: Apr 2005
Location: NJ

Look at this thread in this forum:
http://www.diyaudio.com/forums/showt...threadid=56327 He wrote a program that allows you to create spice models from an image of the tube curves, for diodes and triodes. I used it, and it works well. 
6th July 2005, 11:32 PM  #10  
diyAudio Member
Join Date: Feb 2005
Location: Zagreb

Quote:


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