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2nd November 2017, 06:37 AM  #1 
diyAudio Member
Join Date: Sep 2010

Problems with Multisim tube models
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. 
2nd November 2017, 07:02 AM  #2 
diyAudio Moderator

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.

3rd November 2017, 02:52 AM  #3 
diyAudio Member
Join Date: Sep 2010

Seems like it might be the right way to go.
I made some tests yesterday and everything works fine "as is" but it is very very slow. I estimate it to go a thousand times slower than I'm used to. Made some tests and found that this line have a very big impact on the speed. "BIAK A K I=URAMP(V(IK,IG)URAMP(V(IK,IG)(0.00049917061*URAMP(V(A,K))^1.5)))+1e10*V(A,K)" Something with this exponent (in red) causes the speed issue. I tried to decrease it one step at the time 9, 8, 7... The speed was equally slow all the time until I reached 3, then it released into full speed as I'm used to. It felt like a on/off switch in speed. I feel that this equation goes into stall for some reason and have no clue why. Something in the calculation apparently doesn't fit Multisim 13. It runs, but extremely slow and with wrong result if I put in anything but a 10, so it need to be 10. If I set a 4 it runs approx. 500 times slower instead of a 1000 times. Any specialist out there that have a clue what's going on ? The same type of exponential works fine and have no impact on the speed what so ever. These lines works fine with no issues with the exponent: "BM1 M1 0 V=(0.028826571*(URAMP(V(A,K))+1e10))^0.90897681 BM2 M2 0 V=(0.622671*(URAMP(V(GG)+URAMP(V(A,K))/13.089625)+1e10))^2.4089768 BP P 0 V=0.00087237591*(URAMP(V(GG)+URAMP(V(A,K))/21.021735)+1e10)^1.5" 
3rd November 2017, 03:35 AM  #4 
diyAudio Member
Join Date: Sep 2010

Tried a model from Norman Koren (8 parameter) in Multisim 13 and run into the same slow performance (1/1000 of normal speed) with this line:
"Bp P K I=(0.1377434031m)*uramp(V(P,K)*ln(1.0+(0.3680995655)+exp((3.754409336)+(3.754409336)*((36 .96361454)+(251.1379958m)*V(G,K))*V(G,K)/sqrt((30.10332346)**2+(V(P,K)(1.996524827))**2)))/(3.754409336))**(1.222404059)" Shifted the "**" to "^" and it run at full speed with expected result. 
3rd November 2017, 04:38 AM  #5 
diyAudio Member
Join Date: Sep 2010

Sorry for bothering you again. but what I wrote earlier have no value.
Found that the problem are earlier in the equation. I removed the last part of the equation all together... From: "BIAK A K I=URAMP(V(IK,IG)URAMP(V(IK,IG)(0.00049917061*URAMP(V(A,K))^1.5)))+1e10*V(A,K)" To: "BIAK A K I=URAMP(V(IK,IG)URAMP(V(IK,IG)(0.00049917061*URAMP(V(A,K))^1.5)))" Both runs very very slow. Both with what appears to be correct result. But this runs fast at normal speed but with wrong result: "BIAK A K I=URAMP(V(IK,IG)URAMP(V(IK,IG)(0.00049917061*URAMP(V(A,K))^1.5)))+1e3*V(A,K)" I'll take a break from this... 
3rd November 2017, 07:15 AM  #6 
diyAudio Moderator

Instead of using "^" for the exponential, try the "PWR(x, y)" function.

3rd November 2017, 10:32 AM  #7 
diyAudio Member
Join Date: Sep 2010


3rd November 2017, 12:50 PM  #8  
diyAudio Member
Join Date: Sep 2010

Quote:
By removing the first URAMP command everything is up and running as fast as the tube models that are included with Multisim 13. Original equation: BIAK A K I=URAMP(V(IK,IG)URAMP(V(IK,IG)(0.0038690245*URAMP(V(A,K))^1.5)))+1e10*V(A,K) Modified equation: BIAK A K I=V(IK,IG)URAMP(V(IK,IG)(0.0038690245*V(A,K)^1.5))+1e10*V(A,K) This is the only change made compared to Ayumi's original model. 

3rd November 2017, 04:18 PM  #9 
diyAudio Moderator

That's strange...

3rd November 2017, 06:59 PM  #10 
diyAudio Member
Join Date: Sep 2010

Might be a bug. Seems like the timestep are set extremely low when the equation starts with URAMP. The trial circuit I have used get the timestep to 7.8125 pS instead of 10 uS as it sould be. Thats a lot of extra calculations. I assume you have a lot of experience since you have been in this thread for a long time, so I would like to ask if Ayumi's models are considered to be the most accurate and the closest to the real thing? ...or are there any other libraries of vacuum tube spice models you would recommend to start with. Wayne Clay aka cogsncogs Norman Koren (8 parameter) Rydell Duncan Maybe something else? 
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