  Certain equations with integral constraints have as solutions time-periodic
pulses of a field-like unknown while a current-like unknown oscillates
periodically with time. A general asymptotic theory of this phenomenon, the
generalized Gunn effect, has been found recently. Here we extend this theory to
the case of nonlinearities having only one stable zero, which is the case for
the usual Gunn effect in n-GaAs. Our ideas are presented in the context of a
simple scalar model where the waves can be constructed analytically and
explicit expressions for asymptotic approximations can be found.
