Here is simple Java Applet/App parameter finder. It needs triplet-array of values Vp,Ip,Vg representing points on plate curves, as input. Source code is provided.
Paint model curves over real curves. This approach allows to build models by aligning curves of an image you download off the web displaying published tube curves, with model curves which you change in real-time with slider controls. Models covered are: Koren Improved Triode, Koren Improved Pentode, Polynomial Ex models.