This paper deals with measurements of vacuum tubes to improve models and guitar amplifier simulations. A measurement device has been created. A first set up is dedicated to study the static regimes of real dual triodes 12AX7s. A second one is used to study the dynamic regimes mainly involved by parasitic capacitances. Characterizations of 12AX7s are obtained, including general triode parameters displayed in datasheets and measured parasitic capacitances values. They give quantitative elements to compare the behaviour of real tubes in guitar amplifiers, as tube sellers do. By using these measures, existing mathematic triode models have been compared with new models, developed to match real tube behaviours. These comparisons lead to define a new model which is more accurate than the usual Norman Koren's one. This model includes grid current modeling, dependent on plate-to-cathode and grid-to-cathode voltages around triodes. Parameters have been estimated from measures on both new and warn real tubes in our disposal. These results have been successfully used in real-time multi-stage guitar amplifier simulations.