A new effect, viz., the oscillatory dependence of the collector current on the diameter of the diagram confining the electron flow from the emitter to the collector, is considered. Such a dependence is due to a change in the position of conducting subbands of the diaphragms upon a change in its diameter. It is also shown that the collector current contains a noticeable interference component (associated with the Aharonov–Bohm effect and corresponding to the mixing of conduction channels of the quantum diaphragm) in the case of a strong mismatching of electron states outside and inside the diaphragm. ©1997 American Institute of Physics.