Here the water jacket on the tube is visible protruding out of the cavity.
Filament voltage for the 7289 should be set to 6.0 volts using the jumpers on the control board.
The coiled coolant lines (12 to 24 inches on each side) provide enough resistance to keep the high voltage leakage current low (about 10 micro amps with new distilled water). When it rises to about 50 micro amps, it's time to change the water (about 3 months).
You don't need much airflow from the fan here. In fact, it really isn't necessary to use one.
The control above the coolant connectors sets the bias level.