  The IceCube Collaboration is investigating various types and manufacturers of
photomultiplier tubes (PMT) for possible use in future optical modules. This
report presents characterization results for two different types of HZC
Photonics PMTs: the 3.5 inch XP82B20D and the 9 inch XP1805D. The results are
in good agreement with the specifications as provided by the manufacturer. In
addition, excellent noise behaviour is observed at the low temperatures
relevant for possible use in IceCube optical modules.
