  We perform a calculation of the linewidth of a micromaser, using the master
equation and the quantum regression approach. A `dephasing' contribution is
identified from pumping processes that conserve the photon number and do not
appear in the photon statistics. We work out examples for a single-atom maser
with a precisely controlled coupling and for a laser where the interaction time
is broadly distributed. In the latter case, we also assess the convergence of a
recently developed uniform Lindblad approximation to the master equation; it is
relatively slow.
