The following diagram depicts how a PMT operates in the two-wire probe configuration.
The probe wire must supply dynode resistor string voltage while simultaneously providing
signal pickoff for counting.  While we show the dynodes as "grids" they are more like "cathodes" in
a triode.  They *will* source current pulses into the dynode resistor string.  For this reason
the upper dynodes must be bypassed to ground so that they are not pulled upwards with each
photon current pulse.  There is no bypassing at the anode because this is where the signal is tapped off.
Failure to bypass properly will result in little or no signal output from the PMT.  Because the anode
"sinks" current the output at the signal pickoff is a  negative-going pulse. For this scheme to work
properly the anode load resistor must be large enough to provide a decent pulse amplitude but small
enough to avoid excessive voltage drop while supplying dynode resistor string current.  Typical values
for the anode load are in the 1 Meg ohm range.  Typical values for the dynode resistor string are in
the 5 Meg to 20 Meg (each) range. Dynode resistors need to be substantially larger than the anode resistor.
Upper dynodes should be bypassed to GND.  Placing bypass caps across dynode resistors is a way to lower
capacitor voltage rating but must still have at least one bypass capacitor to GND.

If you take a look at the R1307 hookup diagram here you'll see
that I've modified the R1307 subassembly for the exact same two
wire configuration described above. Another example of conversion
of an R1538 subassembly for two-wire operation can be seen here.
Study these two examples and you'll see the similarities.
 

The diagram above is also a good tutorial on the electrical behavior
of a PMT.  They all work this way.  Only the number of dynodes
and the max voltage changes.  They are friendly animals....give them
a try.

Remember - NEVER apply full voltage to a PMT in any ambient
lighting whatsoever.  You can apply drastically reduced voltages
safely...like maybe 100-200 volts for a 900V tube.  This is because
the gain of a PMT varies exponentially with applied voltage.