• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Does anyone know of an LTSpice model for 12B4?

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A guy named David Heiser has written an article on modeling tubes using Koren's models. You can read about it here:

http://www.daheiser.info/VTT/TEXT/vacuum tube characteristic equations.pdf

On page 24 he mentions the 12B4, and how he had problems modeling it correctly. Nonetheless, here is a spice model based on the values he presented:

.SUBCKT 12B4 1 2 3 ; P G C; NEW MODEL
+ PARAMS: MU=7.5 EX=1.23 KG1=290 KP=48 KVB=280 RGI=1000
+ CCG=5.5P CGP=5.5P CCP=2.0P ; ADD .7PF TO ADJACENT PINS; .5 TO OTHERS.
E1 7 0 VALUE=
+{V(1,3)/KP*LOG(1+EXP(KP*(1/MU+V(2,3)/SQRT(KVB+V(1,3)*V(1,3)))))}
RE1 7 0 1G
G1 1 3 VALUE={(PWR(V(7),EX)+PWRS(V(7),EX))/KG1}
RCP 1 3 1G ; TO AVOID FLOATING NODES IN MU-FOLLOWER
C1 2 3 {CCG} ; CATHODE-GRID; WAS 1.6P
C2 2 1 {CGP} ; GRID-PLATE; WAS 1.5P
C3 1 3 {CCP} ; CATHODE-PLATE; WAS 0.5P
D3 5 3 DX ; FOR GRID CURRENT
R1 2 5 {RGI} ; FOR GRID CURRENT
.MODEL DX D(IS=1N RS=1 CJO=10PF TT=1N)
.ENDS

It is a PSpice model, so it should work LTspice as well.
 
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