Perform a visual check of the exterior of the photomultiplier tube, base and cabling.
Is there any sign of damage to components?
Are the connectors secure on the cables?
Are the connectors secure on the base?
Do the cables mate smoothly with the base?
Are any screws loose, or are they all tightened sufficiently?
Is it possible to open the base?
Visually check for damaged wiring and components.
Are any screws loose, or are they all tightened sufficiently?
Do the solder joints look good?
Is there any sign of corrosion?
Is there any sign of parts over heating? Burnt components or circuit board?

Do you know what the base circuit is supposed to be?
What is the maximum voltage that can be applied to the base?
Positive or negative high voltage?
Are the high voltage ground and the signal ground connected to each other?
Is the connection direct, or through a resistor?
Verify that connection exists by checking the resistance between external connectors on the base.

What power supply will you be using?
Does it have a maximum current of 5 milli-amp or less? If not, you will need extra paperwork.
Does the power supply need a special adapter to connect to the base? If so, you will need to have the setup approved.
Is the high voltage power supply ground connected to the local earth/safety ground? If not, you will need to have the setup approved.

What are you plugging the signal into?
Is the shield of the signal cable going to be floating, or tied to earth/safety ground?
If what the signal is plugged into is floating, you will need to have the setup approved.
When physically handling the base or phototube the high voltage supply should be turned off.

-- If you can't answer any of these questions, stop and contact an expert. --

-- If anything is amiss, stop and contact an expert. --