Curves created with µTracer and
Tube-Model with ExtractModel Software

 
Nice tube, the two system are equal                      Bad tube, the two system are not equal

Measurement-Data with µTracer

       
ExtractModel Software                                                   Comparison of µTracer data / tube model

12AX7 LTspice tube model measured with µTracer and created with ExtractModel Software

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LTspice 12AX7 Tube Model                     LTspice Tube Test

Original 12AX7 tube curves from Sylvania compared with the curves of a
12AX7 Sylvania Tube measured with µTracer and Tube Model created
with ExtractModel Software and Tube Model tested with LTspice