Here are some documents that I find while I search for suitable sockets, should be some good information source to read:

1:   http://nemu.web.psi.ch/doc/manuals/device_manuals/PhotoMultiplier/Photonis.pdf
//a good catalogue of many different types of PMT, including the functionning details of the FMS base that we are currently use on page 48.

2.   http://www.chem.ucla.edu/~craigim/pdfmanuals/catalogs/Hamamatsu_PMT_Catalog-Handbook.pdf
// also a catalogue of PMT by the company named Hamamatsu, noticed that from page 42 to 47 are about the 51 mm PMTs, resemble to the one that we are using currently.
// The E678-19E and E678-19F sockets may work for our FMS socket, while the E678-19D and E678-20A has larger diameter for the pins, the E678-20A type may works for the CDF base. (Still in searching for the place to sell these sockets)

3 .  http://psec.uchicago.edu/links/pmt_handbook_complete.pdf
       http://neutron.physics.ucsb.edu/docs/High_energy_PMT_TPMO0007E01.pdf
// some handbook of the basics and application for PMT.