The 27M1 photomultiplier was used as a noise source in military jammers. We have the more sensitive cousin of this tube as well. See931B. Photomultipliers are cold cathode devices.
The light enters this photomultiplier from the side onto the grid like structure. These grids are called dynodes and a photon falling on them will release secondary electrons. These electrons are accelerated into the next dynode and further electrons are released. In this way amplification factors of many thousands are possible.
In this case with an anode voltage of 100 V and a cathode current of 0.025 mA the gain is 1,000,000 and the sensitivity is 10A/Lumen at a wavelength of 420 nM.
The light entry window with the first cathode behind the wires across the window.
The wires that pass in front of the photocathode.
The ceramic top support. The electrode supports are held in blace by being bent over.
The wide glass tube envelope is 29 mm in diameter and, excluding the 11 base pins, is 75 mm tall.
References: Data-sheet. Type 27M1 was first introduced in 1954.