CircuitMaker Vacuum Tube model

[Steen Bentzen]

Can anyone explain the vacuum tube model parameters in CircuitMaker 2000. Below the original 12AU7 model.

*Vacuum Tube Triode (Audio freq.) pkg:VT-9 (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 1.6E-12
C2 3 1 1.5E-12
C3 1 4 0.5E-12
R1 3 5 10E+3
D1 1 2 DX
D2 4 2 DX2
D3 5 4 DX
.MODEL DX D(IS=1.0E-12 RS=1.0)
.MODEL DX2 D(IS=1.0E-9 RS=1.0)
.ENDS X12AU7

I think that I have found some of the parameters:

?=Don't know

*Vacuum Tube Triode (Audio freq.) pkg:VT-9 (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 1.6E-12 = Grid cap.
C2 3 1 1.5E-12 = Grid-Plate cap.
C3 1 4 0.5E-12 = Plate cap.
R1 3 5 10E+3 = Ri
D1 1 2 DX = ?
D2 4 2 DX2 = ?
D3 5 4 DX = ?
.MODEL DX D(IS=1.0E-12 RS=1.0) = ?
.MODEL DX2 D(IS=1.0E-9 RS=1.0) = ?
.ENDS X12AU7

[Robert McLean]

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.

[Robert McLean]

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.

[fscarpa58]

d3 with R1 (badly) models grid current

Federico

[Steen Bentzen]

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 build-in models and the simulation results are ok and within what you can exspect.

Steen

[fscarpa58]

Hi Steen

I know it's a simple model, but i works ok.

However, do not use that model for distorsion prevision, analisys or optimization.

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

[ilimzn]

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).

[Steen Bentzen]

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

[wa2ise]

Look at this thread in this forum:
Vacuum tube modeling software - beta testers wanted
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.

[ilimzn]

Originally posted by Steen Bentzen
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

Circuitmaker IS PSpice, speciffically, a front end to a speciffic variant of spice 3F4. There are very few simulators that do not use the spice engine.