Saving another PNC-1

This area is for discussions involving any fusion related radiation metrology issues. Neutrons are the key signature of fusion, but other radiations are of interest to the amateur fusioneer as well.
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Jim Kovalchick
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Saving another PNC-1

Post by Jim Kovalchick » Thu Jul 03, 2014 7:19 pm

The first neutrons from Mike's fusor in our basement were measured with a beautiful old PNC-1. The old Eberline proved to be very trusty. We even took it on the road to measure neutrons at the University of Maryland Research Reactor. Somehow, on the return trip, it fell over in the backseat and bumped itself on. We didn't discover this for days, and as it turns out the long time powered up was too much for it, and neutrons no longer moved the needle.

I am a sentimental historian type, and I vowed to repair it. Eventually, I found some free time and started in on it. It didn't take long to determine that there wasn't any potential at the detector. To make sure everything else was okay, I pulled the high volt supply and disconnected the detector so I could install a calibration pulser at the detector jack. Using the pulser I was able to verify that the discrimination, counting, and meter circuits were working properly. So "all" I had to do was fix the HV supply.

I was concerned that the transformer or corona regulator tube would be bad, and Lord knows were I would find replacements. I do get lucky now and then, and as I examined the HV module, I saw some obvious corrosion on one of the rectifier diodes. I removed it to find one end essentially rotted off. The diodes are obsolete 1N3285's. Eberline used lots of these in their detectors in the '60's and I am sure I could find someone to sell me original parts for some silly price, but instead I just replaced them both with 18 cent 2500 V rectifier diodes from Mouser.

I put the new diodes in today, and our old PNC-1 is telling us about neutrons once again. The background is a tad bit high, but a tweak of the discriminator can probably fix that.

Thank you Richard for providing enough inspiration to get me to finish this repair. :)
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Richard Hull
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Re: Saving another PNC-1

Post by Richard Hull » Fri Jul 04, 2014 4:06 pm

Great Story Jim! I love bringing good old gear back on line. You have inspired me to tell a recent tale of woe and ultimate victory. (in a separate post that I will pull together.)

I commonly use 2kv piv diodes of the ultra fast type to replace old diodes of the 50's and 60's. This always boosts the output voltage, but that is often a good thing and readjusting the supply, if variable, is the solution. In your case, just tweeking the discriminator was just as good. I love those little Eberline sqwauk boxes, like the one in the pix. Their design is inspiring. I learned a lot from the contained schematic. A bit of genius.

I had three PNC-1s but sold one recently and have two working units as backups although with the (4) 3He tubes I keep as spares for my current system counter, I can't image going back to my old BF3 PNC-1's with their tiny Nancy Woods tubes. Still, They were my main guys back in the early days, once I cast off the Bicron BC-730 PMT systems.

I can remember when double background on those old guys meant significant fusion. I also remember the first time I saw the needle go upscale and stay there. This was near the end of fusor III's life back in 2001 at 200k neuts per second. For fusor IV I decided to use one of the long 4 ATM, 3He tubes that I had bought from Don Orie in 2000. Wow! What a differential! Instead of 300+ CPM on the PNC-1s, I now work off 10,000++ cpm on the large 3He tubes. You've seen it in action, of course, at HEAS each year you have been here.

Good work, again, on fixing your PNC-1.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Paul W Fontana
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Re: Saving another PNC-1

Post by Paul W Fontana » Tue Feb 20, 2018 6:05 pm

Does anyone have a schematic for the PNC-1, and/or some troubleshooting tips? We found four of these in the back of a cupboard dating back at least to the 1970's, but none of them are in working order. Some students are trying to see if they can refurbish at least one.

-- pwf

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Jim Kovalchick
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Re: Saving another PNC-1

Post by Jim Kovalchick » Tue Feb 20, 2018 6:28 pm

I have never seen a schematic or manual.

There are a few common issues.

1. Tube failure - To test for tube failure, attach the tube to a different device like a Ludlum 2000 scaler. Adjust the voltage to 1400 to 1600 and use a 1.5 mV threshold. See if you can get some counts. You can also check to see if your device is putting out high voltage

2. High voltage failure - If there is no high voltage, locate the high voltage card. It is removable after taking out a couple screws. Examine the board for obvious signs of faults. The diodes fail visibly.

3. Counting circuits - with the high voltage card out, remove the tube and connect a pulser. You should be able to get the meter to respond. Check all the ranges and adjust them with the range screws at the rear of the board.

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Richard Hull
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Re: Saving another PNC-1

Post by Richard Hull » Tue Feb 20, 2018 10:11 pm

Jim's advice is sage. Corrosion in the battery pack contacts and around old solder joints is common. The most common failure is the HV supply, always an easy fix for an adroit hand. The PNC-1 is easily broken down into its components for easy elimination of modules and components one-by-one such that the problem usually sticks out like a sore thumb.

HV supply voltages are best measured with a 100 megohm impedance digital meter. I have a post here in these forums on turning the 1 megohm free Harbor freight digital meter into a 100megohm impedance meter reading from 0-2000 volts DC.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

Andrew Seltzman
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Re: Saving another PNC-1

Post by Andrew Seltzman » Wed Feb 21, 2018 1:09 am

I have some detailed pictures of PNC1 and PNC4 counters:

PNC1
http://www.rtftechnologies.org/physics/ ... tector.htm
PNC4
http://www.rtftechnologies.org/physics/ ... tector.htm

Unfortunately, I don't have any schematics. There is a link to an eberline PNR-4 manual which might have some similar components:
viewtopic.php?f=19&t=9035
Andrew Seltzman
www.rtftechnologies.org

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Richard Hull
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Re: Saving another PNC-1

Post by Richard Hull » Wed Feb 21, 2018 4:55 am

Nice clean looking items. You either cleaned them to perfection or they had a happy life with people around them who cared.

Many such instruments have an unhappy life with professionals who look upon them as mere tools like a hammer or screwdriver. As they age and better gear comes along they are relegated to a closet where the batteries leak into the case. Finally, they are sold surplus where the new owners are rarely informed enough to use them and virtually never care for them. To find a very old instrument like the PNC-1 in near mint or usable condition is a great joy.

The PNC-1 was never a sensitive counter, but would start to work if a fusor was blasting out about 100,000 fusions per second. Sending one of this meters far upscale meant you were hitting the ball out of the park.

I still have two working PNC-1s a large working snoopy and a PNR log-log on a rem ball. (Bonner Sphere)..... Great old working stuff.

Note: The external connectors, cables and contacts from the instrument to the tube in moderator are a horrible source of constant noise if not kept re-soldered, religiously cleaned and not moving while measurements are being taken. These can make you think you are getting neutrons when you are only getting amplified noise pulses. I have re-worked every Eberline neutron counter's cabling and contacts that I have ever owned. Just a safe bet.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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