ST-360 HV Supply and Counter Unit Repaired

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Dennis P Brown
Posts: 1448
Joined: Sun May 20, 2012 2:46 pm
Real name: Dennis P Brown
Location: Glen Arm, MD

ST-360 HV Supply and Counter Unit Repaired

Post by Dennis P Brown » Sun Apr 23, 2017 6:14 pm

Well, after a few months of doing other things I decided to try and repair my ST-360 again. The first time I damaged the unit I had blown the diode voltage limiter. So, I decided to bite the bullet and replace that component again and not mess with testing - lucky, I ordered three (down to just one, now.) Using my microscope and the finest soldering iron I had, I again removed the previous diode (a very tiny three pin micro-chip) and reinstalled a new one (not too difficult under the high mag of a microscope but positioning isn't fun.)

The ST-360 unit appears to be working again.

To test the scintillation port (which feeds into the special amp using the voltage limiting diode chip) for the unit I installed my scintillation detector (designed for a Ludlum Geiger counter), set the voltage and let it count the standard room background level (102 counts/min.) This was the same value I have gotten in the past - that was a good start. Then I used my uranium sample and it gave a reading of about 320 counts/min. Again, this agree's closely with past tests.

Aside: Having a uranium sample is extremely useful for calibration testing to give a clear signal compared to background. I would suggest that someone considering getting or building a detector use this method to confirm operation - useless for neutrons except for very high end counters but very useful for testing standard geiger and scintillation units with its daughter products/gamma's.

I keep my fusor operational (once a week I do a run down to 10^-6 torr) so next week I might do a fusor run with deuterium and see if my Russian made tube is still working; the issue last time that damaged my ST-360, I believe, was either the commercial three-way co-axial connector failed (big time), and/or my voltage divider wasn't sufficient; one of these apparently killed the diode limiter. I have since made new and better units myself and installed them.

Even if the Russian tube still works (and really, I don't see why it wouldn't) I have all the equipment needed to assemble a proper neutron scintillation detector - the special plastic, a photo-multiplier tube, and a high voltage feed supply/coupler circuit board so I just need to hook it all up and package the stuff together. After I install a co-axial cable output I should be able to test it with the ST-360 with the fusor running. However, that project may be a few months since I have a lot of other projects and many other issues/jobs/work to do. But it is very nice to have repaired the ST-360 again and have it available - a good counter/high voltage feed system with display is very nice. In any case, I will strive to be far more careful with the unit from now on ...lol. Lesson, I hope, better learned ... .

User avatar
Dennis P Brown
Posts: 1448
Joined: Sun May 20, 2012 2:46 pm
Real name: Dennis P Brown
Location: Glen Arm, MD

Re: ST-360 HV Supply and Counter Unit Repaired

Post by Dennis P Brown » Sun Apr 30, 2017 5:25 pm

Quick update - either my ST-360 is now very unstable (but works well as a gamma ray detector) or else my new neutron detector connectors (rather complex, unfortunately) to the neutron detector tube are poor or both. Not gonna get any results until I build a low voltage, low noise system or build my neutron photo-multiplier ... delays again.

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