  A family of type IIB superstring backgrounds involving Ramond-Ramond fields
are obtained in ten dimensions starting from a K-model through a generalization
of our recent results. The unbroken global $SL(2,R)$ symmetry of the type IIB
equations of motion are implemented in this context as a solution generating
transfromation. A geometrical analysis, based on the tensor structure of the
higher order $\alpha^{\prime}$ terms in the equations of motion, is employed to
show that these backgrounds are exact.
