  The mobility edge is extracted from a non-perturbative analysis of F.
Wegner's real matrix ensemble (RME), $N$-orbital model of electrons with broken
time-reversal invariance moving in random potential. The replicon fluctuations
around the zero-dimensional (0D), single metallic grain saddlepoint, are shown
to destabilize diffusive regime beyond the low energy limit yielding a precise
criteria of localization in terms of a single scaling parameter.
