A systematic study of large PMTs for the Pierre Auger Observatory

In order to select the most suitable Photomultiplier Tubes (PMTs) for the surface detectors of the Pierre Auger Observatory, we have performed extensive tests on large PMTs from three different manufacturers: Electron Tubes Limited, Hamamatsu Photonics, and Photonis Imaging Sensors. We have developed specialized instrumentation to accurately measure the PMT characteristics such as gain, dark current, single photoelectron spectrum, dark pulse rate, afterpulse ratio, quantum efficiency, and linearity. The instrumentation and techniques used for these measurements and their results are reported.