A single-channel photomultiplier tube having a sealed envelope, of which one wall includes an internal face having a concavity with a central axis, turned toward the inside of the tube, having a plane of symmetry and containing a photocathode, inlet optics including electrodes, an electron multiplier including a plurality of dynodes, an anode, and a mechanism connecting the dynodes, the photocathode, electrodes of the optics, and the anode, at their respective operating voltages. The electron multiplier is composed of parts physically distinct from one another, and having between them a symmetry of revolution with respect to the central axis of the concavity.