The title compounds have been synthesized and studied with a view to stabilize the 123 structure and achieve single phase formation. Single phase and high TC are obtained with Sr content as low as x=0.1 in the case of Yb. The single phase region extends only up to x=0.5, in contrast to the Sr substituted Y-123 system wherein the single phase region has been established up to x=1.2. The TC, zero decreases systematically with increase in x. Preliminary results of thermopower on two of the single phase compounds (x=0.1 and 0.2) show a negative thermopower at all temperatures above TC with temperature dependence similar to that of Y-123. In the case of Lu, Sr substitution does not completely stabilise the 123 phase for any x. However, the quantity of the 123 phase is increased significantly for x=0.4 -0.5 when compared to x=0.0. Structural, electrical and magnetic data are discussed. © 1992.