Peter emailed me with a question about Geiger Counters.\u00a0 With his permission, I’ll quote his questions in the paragraph below and answer them following.<\/p>\n
it\u00b4s Peter again – a few weeks ago I purchased a good, sensitive (and fully functional!!) Geigertube for measuring background radiation – the only problem is that it requires 1000 Volts. Of course I looked at Charles Wenzel\u00b4s page –> http:\/\/www.techlib.com\/science\/geiger.html<\/a>
\nI built the supply with the single 10 mH choke first, cause I hoped being able to modify it appropriately, but I wasn\u00b4t able to get 1000 Volts out of it using 5 Volts \ud83d\ude41 . There are other versions with a transformer capable of higher voltages using only about 3 or 5 Volts – I\u00b4d build them at once if I only knew what type of transformer he means and how to get it (or build it). Wenzel describes it as “a <\/strong>1:1 600 ohm audio isolation transformer” or “phone xformer”. What is this? Can I build this myself? Have you got any tips for me?<\/span><\/p>\nAs always I\u00b4d really appreciate your expert advice!<\/p><\/blockquote>\n
Wenzel’s Techlib has some very interesting projects, especially when it comes to radiation detectors.\u00a0 I would trust his designs and I would not be afraid to build them, knowing that he has experimented with them and has a good grasp of their performance.\u00a0 Having said that, I haven’t done any radiation detector projects and I do not know if his or others work.\u00a0 I do know that from what I’ve read, the typical Geiger tube requires a very small current, microamps if I remember correctly.\u00a0 So the power supply does not have to deliver much power.\u00a0 The tube has a resistor in series, and this has a very high value, might be a megohm or so.
\n<\/span><\/p>\nA quick and simple way to\u00a0 build a high voltage power supply is to use the flash circuit from a disposable camera.\u00a0 The large capacitor charges up to 300 volts or more, and the circuit draws a lot of current from the AA cell.\u00a0 But by making some changes, the power can be reduced.\u00a0 The circuit is similar to a Joule Thief, but with a high voltage winding.<\/span><\/p>\n
I must put a warning here:\u00a0 DANGER!\u00a0 HIGH VOLTAGE!<\/span> You can get a severe shock from this circuit.<\/strong>\u00a0 Make sure you discharge the capacitor before you work on it.<\/p>\n
\u00a0Instead of a rectifier and big capacitor, the output should be changed to use a smaller capacitor of a fraction of a microfarad, but the working voltage must be higher than 1000 volts.\u00a0 The output should be a voltage doubler, which should give at least 600 volts.\u00a0 The base bias resistor should be increased so that the circuit draws much less than the hundred or more milliamps it draws when it’s in the camera.\u00a0 It should draw only as much as it needs to generate the current for\u00a0 the tube, and that could be just a few tens of milliamps.\u00a0 Also, 600 volts is not enough, so the battery supply is increased from 1.5 volts to 3 volts, and that should increase the output to the needed voltage.
\n<\/span><\/p>\nI have very many of the 600 ohm 1:1 transformers used in phone equipment.\u00a0 I have a blog that explains what it is<\/strong><\/a>.\u00a0 <\/span><\/p>\n
There is a Yahoo group called Geiger Counter Enthusiasts<\/strong><\/a>.\u00a0 If you have a Yahoo account you can join this group and find out much more than I can tell you.\u00a0 In order to see this link, you may need to be signed on to your Yahoo account.\u00a0 In its first page it gives links to other Yahoo groups which may be more specialized.<\/span><\/p>\n
Peter, I hope this helps you to solve your questions and get your project on the road.
\n<\/span><\/p>\n
\n<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"Peter emailed me with a question about Geiger Counters.\u00a0 With his permission, I’ll quote his questions in the paragraph below and answer them following. it\u00b4s Peter again – a few weeks ago I purchased a good, sensitive (and fully functional!!) Geigertube for measuring background radiation – the only problem is that it requires 1000 Volts. <\/p>\n
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