I think that the second subcircuit is only a set of parameters to apply to a generic triode model TRIODENH, which you have not got.  Generally, you do not need to know much about the syntax of the netlist of a subcircuit. As it happens, BGG is a B source connected between nodes GG and 0. Others are far more difficult to explain.

Hi all,

 

I need some guidance regarding different models of Valves which are readily available from this and other Web sites.  As an example, I have added 3  12AX7 models below.  I am trying to get them to run in a very simple triode circuit by pasting them directly into a schematic as Spice directives.  ... and then to understand why they are different, in syntax structure and in operation.

 

I have changed the Triode symbol Attributes to .... Attribute is Value,  Prefix is X,   InstName is U1  and  SpiceModel is 12AX7 ... other fields are blank.

 

The first .SUBCKT below runs okay, but I do not understand the syntax eg BGG  GG 0 etc.. I'm okay with the maths. 

 

I cannot find this info anywhere in the LTspice Help, or in my many searches of the Web.  Maybe I'm searching the wrong terminology .... any advice please??

 

Why does the first .SUBCKT model run, but the second one does not.  I get an Error message "Undefined subcircuit triodenh"??

 

Also, why is the syntax vastly different?  eg +PARAMS etc??

 

Thanks, Ian

 

.SUBCKT 12AX7 A G K
BGG   GG   0 V=V(G,K)+0.59836683
BM1   M1   0 V=(0.0017172334*(URAMP(V(A,K))+1e-10))**-0.2685074
BM2   M2   0 V=(0.84817287*(URAMP(V(GG)+URAMP(V(A,K))/88.413802)+1e-10))**1.7685074
BP    P    0 V=0.001130216*(URAMP(V(GG)+URAMP(V(A,K))/104.24031)+1e-10)**1.5
BIK   IK   0 V=U(V(GG))*V(P)+(1-U(V(GG)))*0.00071211506*V(M1)*V(M2)
BIG   IG   0 V=0.000565108*URAMP(V(G,K))**1.5*(URAMP(V(G,K))/(URAMP(V(A,K))+URAMP(V(G,K)))*1.2+0.4)
BIAK  A    K I=URAMP(V(IK,IG)-URAMP(V(IK,IG)-(0.00058141055*URAMP(V(A,K))**1.5)))+1e-10*V(A,K)
BIGK  G    K I=V(IG)
* CAPS
CGA   G    A 1.7p
CGK   G    K 1.6p
CAK   A    K 0.5p
.ENDS
*Ayumi Generic  tube.lib.txt file

 

.SUBCKT 12AX7 A G K
XV1 A G K TRIODENH
+PARAMS: LIP= 1.5 LIF= 0.000016 RAF= 0.076498 RAS= 1 CDO=-0.53056 
+ RAP= 0.18 ERP= 1.5 
+ MU0= 87.302 MUR=-0.013621 EMC= 0.00000111 
+ GCO=-0.2 GCF= 0.00001 
+ CGA=3.90E-12 CGK=2.40E-12 CAK=7.00E-13
.ENDS
*Duncan Munroe Generic  ENHtube.lib file

 

.SUBCKT 12AX7 1 2 3 ; A G C
E1  7 0 VALUE={V(1,3)/KP*LOG(1+EXP(KP*(1/MU+(V(2,3)+VCT)/SQRT(KVB+V(1,3)*V(1,3)))))}
RE1 7 0 1G
G1  1 3 VALUE={(PWR(V(7,0),EX)+PWRS(V(7,0),EX))/KG1}
RCP 1 3 1G    ; TO AVOID FLOATING NODES IN MU-FOLLOWER
C1  2 3 {CCG}  ; CATHODE-GRID
C2  2 1 {CPG1}  ; GRID-PLATE
C3  1 3 {CCP}  ; CATHODE-PLATE
D3  5 3 DX     ; FOR GRID CURRENT
R1  2 5 {RGI}  ; FOR GRID CURRENT
.ENDS           TRIODE
*duncan Munro ???????

 

-- 
OOO - Own Opinions Only
Best Wishes
John Woodgate
Keep trying

I need some guidance regarding different models of Valves which are readily available from this and other Web sites.  As an example, I have added 3  12AX7 models below.  I am trying to get them to run in a very simple triode circuit by pasting them directly into a schematic as Spice directives.  ... and then to understand why they are different, in syntax structure and in operation.

 

I have changed the Triode symbol Attributes to .... Attribute is Value,  Prefix is X,   InstName is U1  and  SpiceModel is 12AX7 ... other fields are blank.

 

The first .SUBCKT below runs okay, but I do not understand the syntax eg BGG  GG 0 etc.. I'm okay with the maths. 

 

I cannot find this info anywhere in the LTspice Help, or in my many searches of the Web.  Maybe I'm searching the wrong terminology .... any advice please??

 

Why does the first .SUBCKT model run, but the second one does not.  I get an Error message "Undefined subcircuit triodenh"??

 

Also, why is the syntax vastly different?  eg +PARAMS etc??

 

Thanks, Ian

 

.SUBCKT 12AX7 A G K
BGG   GG   0 V=V(G,K)+V=V(G,K)+0.59836683
BM1   M1   0 V=(0.0017172334*(URAMP(V(A,K))+1e-10))**-0.2685074
BM2   M2   0 V=(0.84817287*(URAMP(V(GG)+URAMP(V(A,K))/88.413802)+1e-10))**1.7685074
BP    P    0 V=0.001130216*(URAMP(V(GG)+URAMP(V(A,K))/104.24031)+1e-10)**1.5
BIK   IK   0 V=U(V(GG))*V(P)+(1-U(V(GG)))*0.00071211506*V(M1)*V(M2)
BIG   IG   0 V=0.000565108*URAMP(V(G,K))**1.5*(URAMP(V(G,K))/(URAMP(V(A,K))+URAMP(V(G,K)))*1.2+0.4)
BIAK  A    K I=URAMP(V(IK,IG)-URAMP(V(IK,IG)-(0.00058141055*URAMP(V(A,K))**1.5)))+1e-10*V(A,K)
BIGK  G    K I=V(IG)
* CAPS
CGA   G    A 1.7p
CGK   G    K 1.6p
CAK   A    K 0.5p
.ENDS
*Ayumi Generic  tube.lib.txt file

 

.SUBCKT 12AX7 A G K
XV1 A G K TRIODENH
+PARAMS: LIP= 1.5 LIF= 0.000016 RAF= 0.076498 RAS= 1 CDO=-0.53056 
+ RAP= 0.18 ERP= 1.5 
+ MU0= 87.302 MUR=-0.013621 EMC= 0.00000111 
+ GCO=-0.2 GCF= 0.00001 
+ CGA=3.90E-12 CGK=2.40E-12 CAK=7.00E-13
.ENDS
*Duncan Munroe Generic  ENHtube.lib file

 

.SUBCKT 12AX7 1 2 3 ; A G C
E1  7 0 VALUE={V(1,3)/KP*LOG(1+EXP(KP*(1/MU+(V(2,3)+VCT)/SQRT(KVB+V(1,3)*V(1,3)))))}
RE1 7 0 1G
G1  1 3 VALUE={(PWR(V(7,0),EX)+PWRS(V(7,0),EX))/KG1}
RCP 1 3 1G    ; TO AVOID FLOATING NODES IN MU-FOLLOWER
C1  2 3 {CCG}  ; CATHODE-GRID
C2  2 1 {CPG1}  ; GRID-PLATE
C3  1 3 {CCP}  ; CATHODE-PLATE
D3  5 3 DX     ; FOR GRID CURRENT
R1  2 5 {RGI}  ; FOR GRID CURRENT
.ENDS           TRIODE
*duncan Munro ???????

There's no one way to make valve model, so models written by different people are likely to end up different. The test for any model is: how close does it come to predicting the actual behaviour of the real device. That's where you should be directing your curiosity. Models may have varying levels of complexity depending on the accuracy desired by their creators.

As far as syntax... You clearly didn't read the Help thoroughly enough. The syntax: eg BGG  GG 0 etc. is listed in netlist form for each element. So, for example, a B-source - see:

Help > LTspice > LTspice® > Circuit Elements > B. Arbitrary Behavioral Voltage or Current Sources

Syntax: Bnnn n001 n002 V=<expression> ..., where:

"Bnnn" is the instance name. It is the unique reference of that particular element. The first letter of the instance name defines what kind of element definition follows. All B-source names must start with "B". The rest of a name is arbitrary, so long as it is unique. So, "BGG" is the name of the B-source definition that follows.

"n001" is the net name that pin 1 is connected to; "n002" being the net name that pin 2 is connected. So, "GG   0" means pin 1 is connected to net name "GG" and pin 2 is connected to ground, which is universally called "0" in SPICE.

"V=<expression>" is the transfer function of the B-source. So "V=V(G,K)+0.59836683" means that the voltage between "GG" and ground is defined to be V=V(G,K)+0.59836683V greater than the voltage between nets "G" and "K". So "V(x,y)" defines a differential voltage between nets "x" and "y" without any reference to ground.

"<expression>" may contain any function listed in the table that follows on the B-source Help page.

Why does the first .SUBCKT model run, but the second one does not.  I get an Error message "Undefined subcircuit triodenh"??

The error message tells you why the second .SUBCKT failed. It references a separate .SUBCKT called "TRIODENH", but that model is (presumably) not defined anywhere in your netlist. It won't work without it.

Also, why is the syntax vastly different?  eg +PARAMS etc??

The line beginning "+PARAMS:" signifies that everything that follows, down to the "ENDS", is a parameter of the model "TRIODENH" (which is missing). The "+" at the start of each line is a continuation character that means that whatever follows should be netlisted on the same line as the line that preceded it.

--
Regards,
Tony

"V=<expression>" is the transfer function of the B-source. So "V=V(G,K)+0.59836683" means that the voltage between "GG" and ground is defined to be V=V(G,K)+0.59836683V greater than the voltage between nets "G" and "K". So "V(x,y)" defines a differential voltage between nets "x" and "y" without any reference to ground.

..should be:

"V=<expression>" is the transfer function of the B-source. So "V=V(G,K)+0.59836683" means that the voltage between "GG" and ground is defined to be 0.59836683V greater than the voltage between nets "G" and "K". So "V(x,y)" defines a differential voltage between nets "x" and "y" without any reference to ground.

--
Regards,
Tony