The monochromator receives light from the hollow-cathode lamp through the flame together with the light emitted from the flame.  The signal arising at the detector from the flame emission will be rejected and only that from the hollow-cathode lamp will be accepted.  The photomultiplier detector assembly consists of a 0.50 inch, side-on photomultiplier tube with a high voltage power supply, voltage divider and buffer amplifier to measure low level ight signals. The current output corresponds to the intensity of the light falling on its photocathode.  This feeds the amplifier and output device, which displays the measured signals.

            This is what a typical photomultiplier detector tube looks like without the base and resistor ladder network: