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Old 18th April 2008, 04:23 AM   #1
awedio is offline awedio  United States
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Default photomultiplier tube - what is this???

Have a look at this...

http://www.allelectronics.com/cgi-bi...IER_TUBE_.html

Any possible audio uses?
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Old 18th April 2008, 04:58 AM   #2
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Default Photomultiplier

Audio uses - not much. An earlier version of this tube (the RCA 931A) was used as a white noise generator in WW2 counter-measures transmitters. It is mainly used where a very faint light signal needs to be detected.

- John Atwood
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Old 18th April 2008, 06:09 AM   #3
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Other variants of this tube also used to be used to "read" the audio track off film in very early film projectors.

I use a $5000 version as the heart of a laser receiver to look at laser reflections from the sea bottom in a Laser Airborne Depth Sounder survey system. I put down 5 Megawatt, 5 nanosecond wide laser pulses (frequency doubled Nd:YAG laser) and can see bottom reflections from up to 70 metres deep in clear water. One of the boffins here did some calcs and determined that we put out so many 10's of millions of photons in each laser pulse and we need to get 10 of them back for the photomultiplier tube to generate enough signal for us to determine how deep the bottom was.

Photomultiplier tubes are still the most sensitive light sensors known to science.

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Ian
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Old 18th April 2008, 02:54 PM   #4
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They were also used in early computer card readers to read the holes in the card. They were also used in readers that would read those forms you'd fill in the little ovals with pencil marks for the answers...

Dave
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Old 18th April 2008, 05:31 PM   #5
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Variants are also used in some scientific equipment - pulsed flame photometric detectors and that sort of stuff.


Last one I bought was 700 or thereabouts.

Fran
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Old 18th April 2008, 05:40 PM   #6
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Look at the Hamamatsu website -- fascinating stuff -- i bought a bunch of PMT's and unloaded them just a year ago -- you could buy 931's for a few dollars, and sometimes the more exotic devices were almost given away.

got muons?
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Old 18th April 2008, 05:59 PM   #7
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Default Re: Photomultiplier

Quote:
Originally posted by JohnAtwood
Audio uses - not much.
John, that sounds like a challange...

Light-activated tube theremin, perhaps?

Pete
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Old 18th April 2008, 11:06 PM   #8
EC8010 is offline EC8010  United Kingdom
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Photomultiplier tubes are much posher than you might think. Broadcasters used to use them in telecines (film to video) because they provide extremely low noise amplification and high bandwidth. Physicists use them for all sorts of stuff, attempting to detect neutrinos springs to mind (you find a deep mine shaft, fill it with water, and hope to catch the scintillation as a zillions of neutrinos pass through).

You have to be very careful with PMTs. Expose them to light with power applied and they self-destruct. They have enormous gain - 10,000 or more is typical depending on dynode voltage and number of dynodes. Oh, and they're expensive. I replaced a blue telecine tube costing 1500 in 1988.
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Old 18th April 2008, 11:37 PM   #9
fizzard is offline fizzard  Canada
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Also used in combination with scintillation crystals to detect radiation. A PET scanner has a ring of scinillation crystals around the bore of the machines, each with its own photomultiplier. They can detect a single photon of incoming gamma rays.

As far as self destructing when exposed to bright light with the power applied I done this myself with no ill effect.
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Old 19th April 2008, 12:43 AM   #10
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Quote:
Also used in combination with scintillation crystals to detect radiation.
Right. Beckmann used them in their scintillation spectrophotometers, to detect afair alpha and beta radiation from "labelled" molecules.
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