FAQ - Roll your own preamp (Richard Hester design)

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Richard Hull
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FAQ - Roll your own preamp (Richard Hester design)

Post by Richard Hull »

Long lost images from the massive losses of images and files last year still haunts us.
Richard Hester was a brilliant star here in the 2004-2010 time frame. His many useful circuits are now lost.
I have found one of a nice little charge sensitive preamp he designed which I had printed out.
I have scanned it and now post it here as part of a FAQ that I hope to improve upon with testing and more input as time goes by. Unlike other FAQs, I welcome input as long as it is constructive and rigidly to the point. I hope this is be a monument to Richard's work here as it expands and grows within this FAQ.

You can catchup on the original post where the written thread begins in 2010 at.....

viewtopic.php?f=13&t=6092&p=34536&hilit ... ive#p34536

Alas this is a high noise, yet good content running post for 6 Pages!!!!! Whew All great subsequent posted images by Richard are apparently lost forever. (sob) Sadly, this post and it superb effort may have been his swan song. (among his last)

For Nembies
A charge sensitive pre-amp is needed for neutron counter tubes of the 3He and BF3 proportional type. They are very hard to come by, normally, and if you have some electronic skills, know how to properly shield "front end" preamps in an enclosed metal box with short input cables and mount the few front end component in mid air, then this might be for you. All components are still available.

update:

I have altered the original file to include Richards total pre-amp and post amp. I have altered his original a bit for HV bias components with proportional neutron tubes. His original was for a PMT


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HesterCSA_POST_SHAP-UPDT.gif
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
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Re: FAQ - Roll your own preamp (Richard Hester design)

Post by Cai Arcos »

Richard:

I distinctly remember the "Pathetically Simple Charge Sensitive Amplifier". The simplest CSA I've ever seen! I printed it a couple years back but after an hour of searching I'm afraid It is lost to the sand of times...
Searching for it in Google, I found the diagram in Fred's fusor Page (http://www.fusor.eu/monitors.html). It references the original thread where the image is now lost. However, I remember that the image had a brief but comprehensive explanation of the workings of the circuit which I found most helpful.
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Re: FAQ - Roll your own preamp (Richard Hester design)

Post by Jon Rosenstiel »

Missing images in Richard Hester thread have been restored. (Also restored schematic for the "Pathetically Simple Charge Sensitive Amplifier")

Jon Rosenstiel
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Richard Hull
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Re: FAQ - Roll your own preamp (Richard Hester design)

Post by Richard Hull »

Wow! Thank you Jon!!

I will still wring out this simple circuit. I have all the parts.

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
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Re: FAQ - Roll your own preamp (Richard Hester design)

Post by Jon Rosenstiel »

Glad I could help out. I’m going to attempt to restore all of Richard Hester’s missing images/schematics/files.

Jon R
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Richard Hull
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Re: FAQ - Roll your own preamp (Richard Hester design)

Post by Richard Hull »

I applaud your willing to take the project on, Jon. Best of luck in the effort and hope you are successful to the fullest. I hope that Richard is doing well and prospering where ever he is.

I spent the end of the day trying to hand-hew end plates for a small re-purposed box for the pre-amp above. I hope I can squeeze the components in this little box.

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
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Joe Gayo
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Re: FAQ - Roll your own preamp (Richard Hester design)

Post by Joe Gayo »

I converted Richard Hester's design to a PCB with a few modifications (the main one being a high voltage bias connection with a 2nd order RC filter). I'm building a number of these boards late next week. I'm willing to sell completed and tested boards or just the bare boards. Is anyone interested?

I have a picture of the board but it doesn't seem to allow me to add an attachment?
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Richard Hull
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Re: FAQ - Roll your own preamp (Richard Hester design)

Post by Richard Hull »

Joe great work. I would be interested in a bare board or two. Post prices both ways for folks in two places. 1. Here or in posted addition to the original post and 2. in the trading post.

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
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Re: FAQ - Roll your own preamp (Richard Hester design)

Post by Richard Hull »

Please refer to the first posting here as I have updated the diagram using Richards last CSA postamp circuit. (different from his first pass in his original posting)
I have added the full diagram for using the much more sensitive 3H3 or BF3 proportional tubes. His original circuit as for use with PMTs. The bias circuit is critical.

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
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Re: FAQ - Roll your own preamp (Richard Hester design)

Post by Joe Gayo »

Some thoughts:
Before making my iteration I looked through all of Richard Hester's designs and made changes -
- I think the anode connection of D6 is less than optimal since the feedback bandwidth is already pretty low and the performance degrades at higher count rates (I increased the bandwidth in my iteration)
- The FET change seems an unnecessary degradation in performance as this FET is sourced from process 51 and is meant for switching applications and has a low transconductance
- The bias filter should be 2nd order or more
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Re: FAQ - Roll your own preamp (Richard Hester design)

Post by Richard Hull »

Have you posted you circuit diagram? I saw the PCB image. I have a recommendation of the 2N4351A FET front end. (TO-72 case 4 lead) It has a +/-125 volt survival gate to source which is a plus.
The 2N4416 might be nice as well.

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
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Re: FAQ - Roll your own preamp (Richard Hester design)

Post by Joe Gayo »

I updated my post in the Richard Hester thread.
Last edited by Joe Gayo on Mon Oct 19, 2020 8:43 pm, edited 1 time in total.
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Re: FAQ - Roll your own preamp (Richard Hester design)

Post by John Futter »

I'll put up my design
It is a bit more than a preamp as it has post gain / shaping and a discriminator or lower window output to remove low energy pulses or noise for counting modes.
The analize output is suitable for direct connection to a MCA
It uses a cascode at the input to mitigate gate capacitance and raise the input impedance to way above any loading concerns
Shaping is controlled through C12 /R18
C11 should be near the same as input capacitance for best noise performance.
Preamp is senstitive to around 30 electrons of charge
The Test input / output is dual use you can inject a pulser signal here to check shaping / gain etc or a pot to set the discrimator clip level
for battery operation 2 PP9's and a 5 volt regulator (the second PP( for the neg bias for the cascode).
The bias terminal was originally used with minus 400 volts for a CZT detector up rating the capacitor voltage will allow whatever bias on whatever detector.
If using the preamp with a PMT couple to the amp input J1 (CON1) with a 2 pf capacitor
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Re: FAQ - Roll your own preamp (Richard Hester design)

Post by Richard Hull »

The FAQ will benefit all who read it in future with some electronic skills. I will cease working on Richard's design and wait for Joes boards to get here.

The boards I refer to are offered in the thread....

viewtopic.php?f=13&t=6092&start=60

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
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