  Since the early days of experimental particle physics photomultipliers (PMTs)
have played an important role in the detector design. Thanks to their
capability of fast photon counting, PMTs are extensively used in the
new-generation of astroparticle physics experiments, such as air, ice and water
Cherenkov detectors. Small size PMTs ($\leq $ 3 inches diameter) show little
sensitivity to the Earth magnetic field, small transit time, stable transit
time spread; the price per photocathode area is less comparing to the one for
the large area PMTs, typically used so far in such applications. Together with
developments and reduced price of multichannel electronics, the use of PMTs of
3-inches or smaller diameter is a promising option even for nowadays large
volume detectors.
  In this paper we report on the design and performance of a new instrument for
mass characterisation of PMTs (from 1 inch to 3 inches size), capable to
calibrate hundreds of PMTs per day and provide measurements of dark counts,
signal amplitude, late-, delayed-, pre- and after-pulses, transit time and
transit time spread.
