Page 1 of 1

A nice Surplus item to make a Neutron Detector Power Supply

Posted: Wed Dec 06, 2017 10:31 pm
by Dennis P Brown
I obtained a nice surplus item - a 6 Kilo-volt triggering system. While I haven't as yet checked to see if the x-formers work, those components are not critical - so if the HV x-former doesn't function, I already have a larger working version so this will not be an issue. I do like the added step-down/filament x-former, fuse and power cord and that all these systems are already wired together (removing the vacuum tube and bridging will be easy.) I bought this item because I liked the case and HV coaxial feed-thru's, the 6 kV cap and the power cord/step-down x-former all wired in a circuit. (shipping cost more than the item - it is ancient by our standards and was posted as not known whether it still functioned (helps knowing this when making an offer - take note newbie's; most these items can be had for much lower price since most people don't want items that don't necessarily work but for parts, can be a steal having expensive items that do work.)

If the high voltage x-former works (looks in good shape), that will just be a nice extra.

I will remove the 'switching' vacuum tube, install a higher rated resistor inline with the output of the cap, and use this as my new neutron detector power supply. This small x-former will draw far less current so I will be able to convert this to battery power - I have a better inverter, too. The existing high voltage digital supply I have requires too much current for a battery to run it. And while it appears steady, it is a lethal supply and I would like to down grade the power somewhat (not that the cap isn't lethal but it will all be fully enclosed and have a bleed resistor and the output wire will first be fed thru a 100 mega-watt resistor so, the output should be safe.)

This will be my next project for the weekend; if my fusor repairs hold up, I will also fire up the fusor (for neutrons.) Finally, if all this is successful, I will also check to see if I can get my He-3 tube working again.

Aside: the strange "coil" in the front of the case in the lower pic is some type of 'long-wire' delay system, I suspect. Nice Plexiglas tube so, useful, too for other projects. I will extract a few extra components for other possible projects - I build up strange but useful equipment in this manner. Aside to newbie's: always salvage parts - don't throw them away because they can prove valuable later.

The vac tube (even if it works) is of no current use to me. I have no real way to test it nor any interest to do that but again, will save it. I will, this weekend, test the HV x-former system (after I add a bleed resistor to that cap! Always try and think about safety - another important point for people new to HV systems; one careless lapse in judgement can be fatal so try and think ahead and do the extra steps to ensure one is safe.)

Re: A nice Surplus item to make a Neutron Detector Power Supply

Posted: Thu Dec 07, 2017 4:17 am
by John Myers
The vacuum tube is likely a thyratron. Do you see a part number?
The trigger amplifier I got from an auction also has a thyratron, an inductor (though much smaller) and a cap at the output. I believe the cap and inductor are for creating the pulse shape when triggered from the thyratron.

It looks like the xformer at left center just powers the thyratron which would mean the baby blue module on the left would be the HV supply.

Re: A nice Surplus item to make a Neutron Detector Power Supply

Posted: Thu Dec 07, 2017 7:30 am
by Jerry Biehler
Seems massively overkill for a detector power supply. A small ultravolt supply off ebay would be perfect and they run off 12-24v.

Re: A nice Surplus item to make a Neutron Detector Power Supply

Posted: Thu Dec 07, 2017 10:22 am
by Dennis P Brown
Jerry, I will look into those; while I enjoy finding ultra-cheap deals with high voltage systems (for the HV parts and cases, especially), relative to battery operation, your suggestion has both merit and appears more likely to provide a steady voltage.

I have done some limited searching under that heading (specificity for UV power supplies) but most where far too low voltage (I need 2- 3 kV range) and for well over $100; rather pricey compared to my overly large but very inexpensive supply - I may not be searching correctly.

John, your call is very likely correct (and the grey x-former, as you point out, is for powering the vac tube. The blue is the HV supply)

Quick update: the HV x-former is 2.5 kV and both it and the cap work fine. That voltage appears it might be ideal for the neutron tube PS.

Re: A nice Surplus item to make a Neutron Detector Power Supply

Posted: Thu Dec 07, 2017 2:28 pm
by Rex Allers
Another small supply, similar to what Jerry suggested, are the EMCO modules. If you search ebay for 'supply high voltage emco' there are several listed. I have an EMCO F30CT and it is a nice little module. I see one listed now for $55 and the listing has pictures of the data sheet pages. 12V DC in gives 3kV out and it is center referenced so you can use the 3kV (can have either end grounded for + or - output) or you can use the center 'tap' as ground and have both + and - 1.5kV. If you feed in less than 12 V you get lower output voltages and I think that works well down to the hundreds of volts out.

I'm in the process of making a supply for these corona tubes by using a little TDK CXA-L10A inverter made for CCFL lamps. If you search ebay for 'ccfl inverter hantronix' there's a listing that looks like an exact clone of the TDK one I am using. With 5V DC in it makes around 1 kv out at some 10's of kHz frequency. I made a 3-stage multiplier for it and I get well over 3kV DC out of that with 5V in. For a test I loaded it with about 5.5 Mohm and I still got 3 kV out which calculates to over 500 uA. That's much more power than these tubes should need.

I'm still working on what I want. I plan to have feedback from the HV voltage through an Op-Amp to control the input drive voltage. I'll give the Op-Amp a low DC voltage signal that will set the desired HV out. I may write it up if I get it all working right.

Re: A nice Surplus item to make a Neutron Detector Power Supply

Posted: Thu Dec 07, 2017 9:49 pm
by Dennis P Brown
Rex, your points and plans sound good; hope you get your supply working and can post both the results and the "How to" on what you did. These are very useful for others.

While the basic design requires a 100 M-ohm resistor via the paper posted on the forum (or a 50 M-ohm by the seller of my He-3 tube), my real focus is the counter/pre-amp now for the Russian tubes and I want to just get the HV supply done and out of the way.

Since I now have a nice and small +/- 2.5 kV x-former and the large case with all pre-wired connectors (which are designed for high voltage) as well as all the other parts needed, it would make no sense to spend yet more money on an alternate (though smaller) supply. While I have a good (but extremely heavy) HV supply already working I have good reasons to abandon that current digital supply.

While I don't need a battery based HV supply I will leave both space and design components in place for the new supply case so as to enable a battery to be incorporate if needed at a later stage. My primary goal and focus is to get my neutron counters up and working; hopefully, the fusor repairs I performed have fixed all its issues and that part of the effort is complete.

Re: A nice Surplus item to make a Neutron Detector Power Supply

Posted: Sun Dec 10, 2017 7:16 am
by Jerry Biehler
You have to keep an eye out and usually some cheaper ones will pop up. I have some of the 4kv versions and they are very stable. They are used to drive PMTs and other beam optics and stuff in FIBs and SEMs.