Photomultipliers are characteristic devices of particle detectors, used since the beginning of the 20th century, in many experiments around the world. To use them optimally and efficiently in such detectors of broad spectrum of radiation, it is necessary to test, evaluate and characterize them. In the Laboratory of Elementary Particles of University of Guanajuato, it was planned, designed and build a twofold experimental system to evaluate and to study photomultipliers type 9954B-Emi PhotoMultiplier using cosmic rays. It has the following parts: Electronic board (which comprehends phototube feeding voltage divider and reading out analogue signal, and digitalizing circuit) and enclosure dark box (which comprises top and bottom veto counters, based each one on a 10 cm x 10 cm x 0.6 cm plastic scintillator and a Hamamatsu MPPC photodiode S12572-100P, and the material under study). Technical details of this evaluation system and preliminary obtained physical results are presented and discussed.