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Mating Ludlum 2000 and He3 tube

Posted: Mon Jun 22, 2015 11:25 pm
by David Kunkle
I've dropped the bubble detectors because I've located and bought a working Ludlum 2000 and a tested 12" He3 tube from 2 different sources.

Putting this together and getting it working will be a whole new area for me. The Ludlum has a C connector and the tube is BNC. I've also located a "C male jack bulkhead to BNC Female cable connector adapter" . By attaching it to the Ludlum, it looks like it should convert the Ludlum to BNC. I've also located a High Voltage BNC Cable RG-58, 10 feet long. So, question is: will the adapter and cable be all I need to mate the counter to the tube? And does it matter how long the cable is? Does it matter what kind of BNC cable?

Or is it possible to get a cable from Ludlum with the right connectors on each end for less than an arm and a leg- the above adapter and cable would be $65?
Thanks.

Re: Mating Ludlum 2000 and He3 tube

Posted: Tue Jun 23, 2015 5:37 am
by Richard Hull
The ideal is the shortest cable possible within reasonable distance for measurement purposes. If you had a preamp at the head of the tube, the length of the cable might be less critical. The connectors are of little importance although you are pushing the BNC at the tube's voltage which might be as low as 1300 volts or as high as 1800 volts. If the 2000's preamp is suitable, your big hassle will be finding the optimum voltage for operation and then using the discriminator pot to rule out gamma detection.

This is very easy for a regular 3He user, but can be a bit tricky for the new user. Find Carl Willis' videos detailing this process in the FAQ here in this forum to get a feel for this process.

Richard Hull

Re: Mating Ludlum 2000 and He3 tube

Posted: Tue Jun 23, 2015 7:47 pm
by David Kunkle
Called Ludlums and that was almost too easy. Getting a 39 in. C to BNC cable for $59- less than what it would be to scrounge stuff together off ebay. Don't feel like I got gouged anyway like with turbo and vacuum instrument cables.

1750V was optimum when it was tested. Don't know if that translates any to being hooked up to the Ludlum 2000. I will be looking up Willis' video next- thanks for the tip.

Re: Mating Ludlum 2000 and He3 tube

Posted: Sun Jun 28, 2015 5:37 pm
by George Dowell
David Kunkle wrote:Called Ludlums and that was almost too easy. Getting a 39 in. C to BNC cable for $59- less than what it would be to scrounge stuff together off ebay. Don't feel like I got gouged anyway like with turbo and vacuum instrument cables.

1750V was optimum when it was tested. Don't know if that translates any to being hooked up to the Ludlum 2000. I will be looking up Willis' video next- thanks for the tip.
Nice setup David. The Ludlum 2000 is a good instrument. Does it have the 10 turn dial counter on the Threshold control?

Proportional probes need the threshold set as low as 2 millivolts.

George Dowell

Re: Mating Ludlum 2000 and He3 tube

Posted: Mon Jun 29, 2015 2:40 am
by David Kunkle
No, it just has a pot for the discriminator. I believe it's a model somewhat older than the one you mentioned with the threshold control.

Re: Mating Ludlum 2000 and He3 tube

Posted: Tue Jun 30, 2015 7:58 pm
by David Kunkle
I found a 6" diameter x 12" length chunk of polyethylene on Zoro for about $65 incl. shipping. I plan on boring it out with a 1 1/2" spade bit to make a moderator. The He tube is about 1 3/8" D and 12" long. That should give me a thickness of 2.25". In case anyone is interested, you need to search by UHMW-PE (not polyethylene). Before I stumbled on that, I almost gave up and went with sheets from Grainger that would have been about $100, giving me a box-like moderator that wouldn't have been the same thickness around the tube like the cylinder will be.