Although high quality single crystals of cuprate superconductors have been available for quite some time, comparing the properties of different crystals often raised more questions than answers. A proper understanding of cuprate superconductivity can emerge only when it will be possible to vary material parameters one at a time. Recently we grow large single crystals of a the (CaxLa1-x)(Ba1.75-xLa0.25+x)Cu3Oy (CLBLCO) superconductor, where it was previously demonstrated that the variable x changes only the Cu-O-Cu buckling angle and bond distance, and hence the superexchange J. The parameter y controls the doping. For each x there is a y in which Tc is maximum; Tcmax(x). We would like to measure J(x) using inelastic neutron scattering and compare it with Tcmax(x). We are planning to start the project with a test run with one crystal of x=0.1.