CHM 56 Russian tube

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Jim Kovalchick
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CHM 56 Russian tube

Post by Jim Kovalchick »

Russian tubes have been discussed quite a bit on this forum, but I'm sure there is still much to learn about them. Here is another bit of experience I thought I would share.

In the last year or so I purchased a CHM 56 tube on ebay for around 100 dollars. It was advertised as a high sensitivity He3 tube that operates in the proportional mode. Ever the sucker for a good neutron tube I thought I would try it.

I am happy to report that I am very satisfied with the tube. It works pretty seamlessly with my Ludlum 2200 even without a preamp. I simply added a resistor and MHV fitting and plugged it in. I buried it in a cardboard tube filled with ground up black HDPE plastic and put it close to my fusor. It seems to like 1400 volts. I initially set the threshold on the Ludlum until it only gave a few counts per minute. During initial exposure to neutrons I found that it counted too many xrays and adjusted the threshold upward until there was clear drop off of detector counts when I pulled it out of the moderator. At this setting I am still getting a few counts a minute background. So I think I found a sweet spot.

Sensitivity wise, I'm very happy so far. Today during a fusor run, it clearly showed fusion in progress at 30 kV and only a couple milliamps when my PNC-1 was barely twitching. Today while I ran my fusor at 53 kV and 15 mA, my PNC-1 very close to the chamber read 3000 cpm. The CHM 56 read around 12,000 cpm.

The CHM 56 is not a long tube. This makes it ideal for a compact fusor system.

This link is to a quick video show my tube and Ludlum arrangement this morning at 45 kV, 13 mA, and about 7000 cpm.

https://youtube.com/shorts/dEAsMKBZqs0?feature=share

Jim K
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JoeBallantyne
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Re: CHM 56 Russian tube

Post by JoeBallantyne »

Jim -

Could you explain in more detail exactly what resistor you added and in what configuration?

DId you put the resistor in series between the MHV center connector (supply voltage) and the tube anode, and then connect the MHV ground connector to the tube cathode? What value and power type of resistor did you use?

Curious minds want to know the details so we can replicate the setup if desired.

I have a Ludlum 2200 and some Russian tubes, so the mods you made are of interest to me.

Thanks.

Joe Ballantyne
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Richard Hull
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Re: CHM 56 Russian tube

Post by Richard Hull »

For those of us who are fortunate to own a Ludlum 2200, you might notice the control settings on the instrument in the video Jim supplied. Windowing is turned "off" (you don't need it) the upper level is set to zero as it is not needed. Only the lower level is set to some value determined by Jim via experiment. Jim is a first rate operator and tuned his tube in rapidly via his quality post above. Read and heed!

A true, good neutron counter detection tube, regardless of type, if set up correctly, will never count over about 5-10 cpm unless you live and work on K12 or Mount Everest! If you count 20cpm background or more, you are not counting only neutrons!
A good neutron tube in or out of a moderator should count only neutrons and lucky catch, cosmic rays. Most all counts on a good setup neutron counter will be cosmic ray event debris. 0-10cpm, as a rule. My PNC-1 counts at best 1 CPM background. (Jim has one too) The Eberline PNC-1 is indeed tough to tickle into operation. (needs a good deal of neutrons to move the needle up scale) This is due to the rather tiny BF3 tube in its small moderator.

The 2200 in the hands of someone "in the know" is quite possibly the best instrument for any nuclear metrologist trying to get ion multiplication tubes working (GM tubes) and proportional tubes set up. (BF3 and 3He tubes). In short, it is a prewired NIM Bin so far as we are concerned. The issue is it uses that @%#$&* C connector! Ludlum must have a brother-law in the C connector biz! A more common HV BNC connector would suffice. However for most here, even a HV BNC is an oddball. Remember, it only takes money or a great scrounge to outfit yourself with all the connectors you will ever need. Hamfests over the years have loaded me up with all manner of oddball connectors for pennies on the dollar. It just takes "seeing at sight". Do not laugh. Seeing at sight is an art and not a given, even if it sounds absurd.

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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Jim Kovalchick
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Re: CHM 56 Russian tube

Post by Jim Kovalchick »

Joe,
I have a low wattage 10 M resistor in series with the tube post. The post in this case is threaded so a couple nuts fastens it on. I don't think the wattage matters. You are just trying to let help the voltage dip a little when the gas discharges in the tube. You may get away without a resistor at all. The Ludlum has a bias resistor in it that is often enough depending on the tube.
Yes, I ground the MHV barrel to the tube wall. Do not solder it otherwise you risk destroying the tube. I have clamped the ground wire to tubes in the past but I think the risk of crushing a tube is too great. I bare a long strip of wire and wrap it around a few times and tape it on with copper tape. I'm sure there are better ways, but make sure the contact is good. Any little bit of noise ruins the integrity of your counts.

Jim K
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Jim Kovalchick
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Re: CHM 56 Russian tube

Post by Jim Kovalchick »

As a follow to Richard's comment I am including a picture of my Ludlum 2200. In this particular one minute background, there were only two counts. The really important control is the threshold. For a proportional tube, this will vary a bit for each tube, and is key to get rid of xrays. For fusors operating at a decent voltage, there are are so many that even at there low energy, detectors get bothered by them. In my case, a somewhat stiff gamma source could not be seen at my initial threshold setting, but lower energy xrays in volume could be. Fortunately, the pulse produced when He 3 grabs a neutron is pretty profound.
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Re: CHM 56 Russian tube

Post by Richard Hull »

When Jim notes the neutron pulse is pretty profound, This can only be seen with the eye on a Digital storage oscilloscope (DSO).
Compared to the fuzzy short hair of an intense gamma source, the neutron pulse will stick out like a sore thumb being a huge spike among the gamma fuzz. It is easily discriminated out of the counting using the lower level setting. ( In this case, the "threshold" setting)

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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