Phase diagrams (T=f(x)) are determined for binary mixtures composed ct two homologous series nOBCAB-nTPCHB. it is shown the immiscibility of the smectic A : of both components. The smectic A, phase of nTPCHB compounds with longer allphatic chain is miscible with smectic A, of 9OBCAB component and involves the dimerization of compounds nOBCAB with short aliphatic chain. The results confirm that investigated homologous series form different kinds of the smectic A, phase.