In this paper, a study of
orthogonal primitive idempotents and minimal ideals in topological algebras with
orthogonal bases has been made. Among other results, a structure theorem for
Banach algebras with orthogonal bases has been proved, similar to Ambrose’s
structure theorem for H∗-algebras in the separable case. Furthermore, a necessary
and sufficient condition is given for Banach algebras with orthogonal bases to be
isomorphically homeomorphic with the Hilbert algebra l2.