In this paper, preliminary experiments to determine the design and construction of a twelve-stage electron multiplier tube, which is operated with high stable gain for the detection of very small ion currents in a mass spectrometer, are described. The simple effective activating method of electrodes made of copper-beryllium alloy sheet was considered with phase diagram, and then electrolytic polishing was used after ?A-phase was separated out by hardening and tempering. The electrodes were also observed with the metallurgical microscope, electron microscope and diffraction. On the operational characteristics of the demountable five-stage multiplier, experiments were compared with electric potential field of its multiplier, which was measured by the conducting sheet method.