Over the July 4 holiday, I took some time to refurbish an old PMT base/preamp I picked up on Ebay for a song. The preamp board inside was on old trashy phenolic, with only one transistor of 2 (germanium, no less)populated. It was ruthlessly ripped out and replaced with a new board incorporating the HV circuitry from the old (HV filter, last dynode resistor plus bypass), plus a new preamp based on the 3 transistor Hamamatsu circuit. Since this base was slated to work with an NaI scintiilator, I didn't think a more ambitious preamp circuit was necessary. I took some digital photos of the resulting assembly,and they will be uo for view when I have time to work on my web site (a first as well).
I brought the base, a Power Designs precision HV supply, and a Bicron NaI scintiilator (ebay again) to work so I would have access to a nice digital scope. Also in the box was a hunk of Uranium ore to act as a check source. With the whole mess hooked together and powered up at 900V, I was gratified to get occasional background pulses of about 1/2V and 1usec long, with occasional monsters going off screen at 1V/div. Things livened up considerably when I brought the check source close to the scintillator. Hurrah! I now have a setup to exercise my NIM components and MCA. Busy times lie ahead....
My First Scintillator
Re: My First Scintillator
Richard -- I follow your foot-steps - can I pick your brain -- please can I have the circuit ( Hamamatsu or otherwise ) of the PMT pre-amp
obliged John
obliged John
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guest
Re: My First Scintillator
The infamous Hamamatsu 3-transistor preamp is archived on Jim Lux's site - http://home.earthlink.net/~jimlux/nuc/index.htm
This site includes a *.pdf file of the preamp and the PMT that came with it. The preamp is a perfect example of a minimum-parts design optimized for the job at hand. It has the advantage of extreme simplicity, and is easy to get working, as long as you stick to the values in the schematic. I built one up on a piece of perf board for grins and had it up and running in about an hour. The compensation cap is selected with NaI in mind (long pulse decay time). This amp could probably be used with BC-720 with a smaller value of compensation cap to match the shorter pulse decay time of ZnS.
Disadvantages: sensitivity to noise and ripple on the negative supply, the gain resistor affects the bias point, bias point is temperature and negative supply sensitive.
If you use a quiet and accurate +/-15V supply, it's not much of an issue, though it still bugs a fussbudget like me.
I have been doing quite a bit of work on preamp topologies for plastic scintillator work, including a few simple improvements on the original Hamamatsu design. When I get some time, I will compile a preamp beastiary and post it.
This site includes a *.pdf file of the preamp and the PMT that came with it. The preamp is a perfect example of a minimum-parts design optimized for the job at hand. It has the advantage of extreme simplicity, and is easy to get working, as long as you stick to the values in the schematic. I built one up on a piece of perf board for grins and had it up and running in about an hour. The compensation cap is selected with NaI in mind (long pulse decay time). This amp could probably be used with BC-720 with a smaller value of compensation cap to match the shorter pulse decay time of ZnS.
Disadvantages: sensitivity to noise and ripple on the negative supply, the gain resistor affects the bias point, bias point is temperature and negative supply sensitive.
If you use a quiet and accurate +/-15V supply, it's not much of an issue, though it still bugs a fussbudget like me.
I have been doing quite a bit of work on preamp topologies for plastic scintillator work, including a few simple improvements on the original Hamamatsu design. When I get some time, I will compile a preamp beastiary and post it.
Re: My First Scintillator
Thanks Richard I look forward to the circuits when you get time to post them John
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Richard Hull
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Re: My First Scintillator
That three transistor pre-amp schematic is one I drewup from the circuit board (reverse design) and distributed over two years ago when I offered a gang of those tubes and amps to the list. Jim Lux bought one at that time and posted all the stuff I sent on his site at that time. I once was awash with those nice little items. I think Tom Dressel or someone actually bought one of those at a hamfest which I originally sold here in Richmond at the hamfest here! Small world.
Richard Hull
Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Tom Dressel
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Re: My First Scintillator
If you are talking about a EMI 9856 PMT, Yes I got it on Ebay about two months ago.
I have it all wired up and in place in my Products For Research PMT housing. I have all the BNC and MHV-BNC connectors, low voltage and high voltage power supplies, pulse generator, blue LED mounted in a light tight PMT mount, SCA, rate meter, counter in a NIM bin. Everything is ready to go, I just need to get some time to hook it all up and test the system. I will post pictures in the IDJ thread.
Tom Dressel
I have it all wired up and in place in my Products For Research PMT housing. I have all the BNC and MHV-BNC connectors, low voltage and high voltage power supplies, pulse generator, blue LED mounted in a light tight PMT mount, SCA, rate meter, counter in a NIM bin. Everything is ready to go, I just need to get some time to hook it all up and test the system. I will post pictures in the IDJ thread.
Tom Dressel
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Richard Hull
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- Real name: Richard Hull
Re: My First Scintillator
Yes. Sorry Tom, I have trouble with events over two months old.. Ha Ha.
You bought your PMT off of someone who either bought it off me at the Richmond Hamfest, one of my Teslathons, or at the Rochester Teslathon I attend yearly. Sorry about the mix up in the details. Those things have really made th' rounds. I think I sold about 25 of those ready to go combos.
Richard Hull
You bought your PMT off of someone who either bought it off me at the Richmond Hamfest, one of my Teslathons, or at the Rochester Teslathon I attend yearly. Sorry about the mix up in the details. Those things have really made th' rounds. I think I sold about 25 of those ready to go combos.
Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment