The Granato-Lücke theory of amplitude dependent internal friction contains a number of parameters, more than can be determined from an experiment. In a polycrystalline specimen all orientations of dislocations towards the external stress are equally probable, and an appropriate integration removes the orientation factors and the fractions of total dislocation length in these orientations. The vibrational entropy is allowed for, and an extension to higher amplitudes is used. In addition, a special experiment allows the determination of the break-away stress of a network length with a single pinning point. Thus the number of parameters is reduced sufficiently. The method is illustrated by an example.