The problem of particles coupled by an isovector pairing interaction is solved by means of a collective treatment. The Hamiltonian and the beta-decay operators acting within the np-subspace are constructed. The procedure reproduces exact results for a schematic model. The realistic calculation of the Fermi amplitude for the double-beta decay of ⁷⁶Ge confirms the current expectation about its smallness relative to the Gamow-Teller decay.