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The 931A is a mass market photomultiplier. It was used as a noise source in military jammers, and in America for automatic headlight dippers. Most recently it has been used by radio amateurs as the front end of sensitive optical receivers.

We have the more sensitive cousin of this tube as well. See 931B

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 photomultiplier is a cold cathode device.

The wide glass tube envelope is 28 mm in diameter and, excluding the base pins, is 72 mm tall.

Reference: Data-sheet & private communication. Type 931A was first introduced in 1950. See also 1950 adverts.

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.