• The effect of Sr–substitution for Ba on superconductivity in (Yb,Ca)(Ba,Sr) 2 Cu 3 O 6 without any oxygen ions in the blocking layer of Cu(1)O chain. • T c increases with increasing Sr–content in contrast to REBa 2 Cu 3 O 7 with T c ∼90 K. • Holes are more likely supplied to the conducting Cu(2)O 2 plane than the blocking layer of Cu(1) through the Sr–substitution. • The highest T c = 73 K is greatly higher than the previous record of 50 K in (RE,Ca)Ba 2 Cu 3 O 6. We have investigated the effect of the Sr-substitution for Ba on the superconductivity in Yb 0.6 Ca 0.4 Ba 2- y Sr y Cu 3 O 6 without O chain forming the so-called Cu(1)O chain in the blocking layer. It has been found that T c increases with increasing y even though no holes are doped through the Sr2+-substitution for Ba2+. The increase in T c is because holes doped by the Ca-substitution for Yb are more likely supplied to the superconducting Cu(2)O 2 plane than the blocking layer of Cu(1) owing to the contraction of the Cu(2)O 2 plane through the substitution of smaller Sr2+ for larger Ba2+. The highest T c onset = 73 K observed for y (Sr) = 0.6 is greatly higher than the previous record of T c onset = 50 K in (RE ,Ca)Ba 2 Cu 3 O 6 (RE : rare-earth element). The reason why it is lower than ∼90 K for RE Ba 2 Cu 3 O 7 is the low hole-concentration in the Cu(2)O 2 plane. [ABSTRACT FROM AUTHOR]