A crucial closed-form Routh–Hurwitz, whose violation indicates imbalance, is derived for local exponential stability of the operating point. Its dependence on the operating inflow is made explicit. For uncertainties involving parametric variables, a conservative interval test is conducted along with an exact test for the physically consistent cases in which the uncertainty enters through one lumped coefficient. As for nonlinear models near equilibrium, a Lyapunov-equation certificate is provided. Stability is lost through a Hopf bifurcation at the critical integral gain. The direction of constant storage area is governed by the first Lyapunov coefficient, which is considered negative (supercritical) for the illustrative parameters and for 99.8% of a random parameter sample. The growth of the resulting oscillation amplitude is comparable to the square root of the gain excess, so that gate saturation is reached at a small excess of the gain. Numerical simulations confirm the predictions where the parameters are illustrative.