I’ve bought a couple of FEU84-5 PMT’s from an eBay seller because I’ve got an occasional low price.

I’ve extensivelly tested them with a 30 dia. 40 lengh (mm) CsI(Tl) crystal. Result? This tube is useless for spectroscopy. FWHM at 662keV vary from 11 to 13% uppon voltage setting! As comparison the same crystal coupled with a FEU85 gives me 7-7.5%. I’ve expected a better result from FEU84-5 because it’s multialkali photokatode is designed to couple with 550nm-light emitting crystals like CsI(Tl). Strange: I’ve obtained better results from FEU85 that’s made for 420nm light.

GENERAL SPECIFICATIONS
Photocathode -  antimony-potassium-sodium-cesium
Optical input - front
The diameter of the working area of the cathode - 25mm 
The number of amplification stages - 12
Wavelengths of maximum sensitivity  -   420-550 nm green light
Dark current  -   < 50 nA
Sensitivity of the photocathode   -   80 uA/lm
Anode sensitivity - 80 A/lm
Life time   -   more than 1000 hours
Maximum Ratings :
Max Voltage -  1900 V
Max anode current - 5 micro A

FEU84-5 and it’s datasheet

It comes into a cardboard envelope with some sponge that starts to disintegrate after 30 years of storage. Nothing to complain… some paper and alcool and I’ve cleaned the tube.

FEU’s box

FEU’s sponge :3

This version of the tube doesn’t have a socket, it have just some teflon insulated wires. This is not bad…there is no need to buy a proper ceramic socket.

End wires

FEU front window