Photomultiplier tube teardown, and speed test - Page 1
Forum section: electronics / general

author: muvideo
author_rank: Frequent Contributor
timestamp: June 21, 2012, 06:03:01 pm
content: This is and old black box I had in the strange things bin.My interest for it resurrected when I was playing with a pulse generator andthen I tried to hook up a led to that... but this is an other story.The black box contains an RCA 931 tube, it's a photomultiplier device,seem it was relatively common back then and it's easy to find someselling on the bay.The “eye”, from here the light enters the sensing side of the tube:Le'ts open it:And here is the old RCA931A in all it's glory:This is the pcb, the opamp suggests that the tube was used for high sensivityapplications, the resistors generate the voltage ladder that supplies the multiplierstages:The box contains also a small lamp, self testing perhaps:The photomultiplier tube is a very interesting device,because it combines high sensivity, high speed andeasy coupling to 50Ohm scope inputs, the onlyrequirement is to have at hand an high voltage supplyof around 1kV.This old tube (the tube itself was build in 1978, butthe datasheet specs are of 1959) is capableof a risetime (well, better call it a falltime)of 2nS and a transit time of 8nS.Let's test it with a pulse generator drivinga small led, the PMT was biased with a voltageof 900V:Another fascinating thing about tubes is thatthey make visible “single events”, drive thetube with high voltage and the output showsrandom single events where an electron getsmultiplied and generate an electron shower onthe output. In this case the event is very fastand this can be a good reference point to calibratethe circuit for maximum speed.I modified the biasing of the electrodes,I adapted the circuit in app note TP-133 from Burle:added some resistors and capaticors to last 4 dynodesstages and shortened as much as possible some ofthe components, now the pulse is much cleaner:the light sourceis an orange led connected to the output of anavalanche pulser:Not bad from an old vacuum deviceFabio.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 22, 2012, 01:48:58 am
content: These devices were used in TV "Flying Spot" slide scanners,in conjunction with special high intensity,low persistence CRTs.They could produce a video signal of considerably higher resolution than the system they were used in.By contrast,the first generation of vidicon slide scanners,were battling to meet Broadcast specs.

author: muvideo
author_rank: Frequent Contributor
timestamp: June 22, 2012, 08:13:43 am
content: Just for fun this tube easily resolved the time of flight of a light pulse over a 6m path:https://www.eevblog.com/forum/projects-designs-and-technical-stuff/fun-with-laser-and-pmt-tube-or-how-much-is-the-speed-of-light-here/As I understand this wasnt a particular high specs one, it's datasheet is here, I was wrong, thedatasheet is from 1950 and not 59:http://tubedata.tubes.se/sheets/049/9/931A.pdfAnd here a pair of interesting appnotes, I adapted the biasing circuit of the first:ftp://ftp.sic.rm.cnr.it/incoming/artov.isac.cnr.it/Maurizio.Viterbini/Public/pmt/Burle2.pdfftp://ftp.sic.rm.cnr.it/incoming/ifa.rm.cnr.it/Maurizio.Viterbini/Public/pmt/Burle.pdfGK, who produces them today? I know of Hamamatsu that has many models in catalogue.I've seen also that there are microchannel based pmt that have very high speed.Fabio.

author: radhoo
author_rank: Contributor
timestamp: June 23, 2012, 08:53:06 pm
content: I'm using a scintillation probe with a NaI (Tl) crystal and a XP2008 modern photomultiplier.Some more details are available here:http://www.pocketmagic.net/?p=1541I recently got an Atten ADS 1102CAL so I'll be able to analyze the probe's output more carefully. For now I've used the PC sound card and I've been able to create a nice gamma spectrography tool, here's a Cs137 source identified with this probe:

author: XynxNet
author_rank: Regular Contributor
timestamp: June 24, 2012, 10:32:14 am
content: If you don't have access to a suitable crystal, go hunting for muons.Get a thermos bottle (those old glasstype ones with the mirror finish inside), fill it with clear water, stick the photomultiplyer tube inside and prevent ambient light leaking in.