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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Detectron Geiger Counter
I recently bought an old Detectron model DG-7 geiger counter. This is from
the early 50's and has three 1U5 tubes inside. Power requirements are 90 volts for the B+, two "D" cells for the tube filaments, and a 4.5 volt bias supply. I went over the unit, replacing a selenium rectifier and testing the tubes. The unit powers up, but generates a steady stream of pulses on it's own, even with the probe detached. The frequency of the oscillation varies with the range selector knob. The probe is working - when brought near a source (a bunch of vaseline marbles) it will produce extra clicks in addition to the stray ones generated by the unit. I've checked all the other components - resistors, capacitors, etc. The only thing I couldn't check is a very small tube, which looks like a cold-cathode rectifier of some kind. I've also tried varying the B+ and bias voltages. And I can't find a schematic, which makes matters worse. I'm not sure what to do next. Any ideas? |
#2
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Detectron Geiger Counter
Chris F. wrote:
I recently bought an old Detectron model DG-7 geiger counter. This is from the early 50's and has three 1U5 tubes inside. Power requirements are 90 volts for the B+, two "D" cells for the tube filaments, and a 4.5 volt bias supply. I went over the unit, replacing a selenium rectifier and testing the tubes. The unit powers up, but generates a steady stream of pulses on it's own, even with the probe detached. The frequency of the oscillation varies with the range selector knob. The probe is working - when brought near a source (a bunch of vaseline marbles) it will produce extra clicks in addition to the stray ones generated by the unit. I've checked all the other components - resistors, capacitors, etc. The only thing I couldn't check is a very small tube, which looks like a cold-cathode rectifier of some kind. I've also tried varying the B+ and bias voltages. And I can't find a schematic, which makes matters worse. I'm not sure what to do next. Any ideas? When the b+ becomes to high, the gas-discharge tubes start oscillating, producing a steady stream of pulses. So start with lowering b+ to zero, and then increase, until either back at 90 volts, or the pulses re-appear. At that point lower the voltage a bit, and re-check with your radiation source. Also there should be a capacitor across the tubes somewhere, If so, check their quality(leakage and value). |
#3
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Detectron Geiger Counter
On Thu, 22 Apr 2010 10:41:19 -0700, "Chris F."
wrote: I recently bought an old Detectron model DG-7 geiger counter. Schematic of the DG-9 model: http://www.curtcass.com/detectron/dg9-sch.jpg Probably quite similar to the DG-7. I went over the unit, replacing a selenium rectifier Replace it with what? Is silicon, the B+ is probably too high. At that age, 99.999999% of the electrolytic cazapitors have high ESR. However, looking at the schematic, there are none. Weird. and testing the tubes. How? With a tube tester? I sometimes work on ancient Motorola radios with pencil tubes. I have to make my own adapter to work in the tube tester. The unit powers up, but generates a steady stream of pulses on it's own, even with the probe detached. Ok, something is oscillating. I have some guesses based on the schematic, but the right way is to get a scope, with a high voltage probe (i.e. 100x) and sniff around for which section is oscillating. My best guess is that since the beast doesn't have any power supply filter capacitors on any of the batteries, and you've probably assembled a mess of power supplies, batteries, and junk to simulate the batteries, you have a fairly high impedance on the power supply lines. Rather than fixing it with a proper battery, find a big fat capacitor (with a suitable high voltage rating), and put it across the power supply leads as close to the circuit (not as close to the battery) as possible. The magic buzzword is "motorboating". The frequency of the oscillation varies with the range selector knob. The probe is working - when brought near a source (a bunch of vaseline marbles) it will produce extra clicks in addition to the stray ones generated by the unit. Good, it's working. http://www.youtube.com/watch?v=U6x5mSp0PeA 0.2mr/hr, about the same as background radiation. (I have the same counter and the one in the video seems a bit insensitive). I've checked all the other components - resistors, capacitors, etc. The only thing I couldn't check is a very small tube, which looks like a cold-cathode rectifier of some kind. Nope. Probably a neon lamp used as a regulator. Photo? I've also tried varying the B+ and bias voltages. And I can't find a schematic, which makes matters worse. I'm not sure what to do next. Any ideas? Google for "Detectron Schematic". http://www.curtcass.com/detectron http://www.curtcass.com/detectron/index2.html -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com # http://www.LearnByDestroying.com AE6KS |
#4
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Detectron Geiger Counter
Chris F. wrote in message
... I recently bought an old Detectron model DG-7 geiger counter. This is from the early 50's and has three 1U5 tubes inside. Power requirements are 90 volts for the B+, two "D" cells for the tube filaments, and a 4.5 volt bias supply. I went over the unit, replacing a selenium rectifier and testing the tubes. The unit powers up, but generates a steady stream of pulses on it's own, even with the probe detached. The frequency of the oscillation varies with the range selector knob. The probe is working - when brought near a source (a bunch of vaseline marbles) it will produce extra clicks in addition to the stray ones generated by the unit. I've checked all the other components - resistors, capacitors, etc. The only thing I couldn't check is a very small tube, which looks like a cold-cathode rectifier of some kind. I've also tried varying the B+ and bias voltages. And I can't find a schematic, which makes matters worse. I'm not sure what to do next. Any ideas? 90V seems low for a GM, is there a step up circuit to 300V or so ? |
#5
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Detectron Geiger Counter
Yes it uses some kind of step-up circuit, and the output to the GM tube is
about 300-400 volts. "N_Cook" wrote in message ... Chris F. wrote in message ... I recently bought an old Detectron model DG-7 geiger counter. This is from the early 50's and has three 1U5 tubes inside. Power requirements are 90 volts for the B+, two "D" cells for the tube filaments, and a 4.5 volt bias supply. I went over the unit, replacing a selenium rectifier and testing the tubes. The unit powers up, but generates a steady stream of pulses on it's own, even with the probe detached. The frequency of the oscillation varies with the range selector knob. The probe is working - when brought near a source (a bunch of vaseline marbles) it will produce extra clicks in addition to the stray ones generated by the unit. I've checked all the other components - resistors, capacitors, etc. The only thing I couldn't check is a very small tube, which looks like a cold-cathode rectifier of some kind. I've also tried varying the B+ and bias voltages. And I can't find a schematic, which makes matters worse. I'm not sure what to do next. Any ideas? 90V seems low for a GM, is there a step up circuit to 300V or so ? |
#6
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Detectron Geiger Counter
Chris F. wrote in message
... Yes it uses some kind of step-up circuit, and the output to the GM tube is about 300-400 volts. "N_Cook" wrote in message ... Chris F. wrote in message ... I recently bought an old Detectron model DG-7 geiger counter. This is from the early 50's and has three 1U5 tubes inside. Power requirements are 90 volts for the B+, two "D" cells for the tube filaments, and a 4.5 volt bias supply. I went over the unit, replacing a selenium rectifier and testing the tubes. The unit powers up, but generates a steady stream of pulses on it's own, even with the probe detached. The frequency of the oscillation varies with the range selector knob. The probe is working - when brought near a source (a bunch of vaseline marbles) it will produce extra clicks in addition to the stray ones generated by the unit. I've checked all the other components - resistors, capacitors, etc. The only thing I couldn't check is a very small tube, which looks like a cold-cathode rectifier of some kind. I've also tried varying the B+ and bias voltages. And I can't find a schematic, which makes matters worse. I'm not sure what to do next. Any ideas? 90V seems low for a GM, is there a step up circuit to 300V or so ? I use an ex military GM tube with ditched 1960s electronics (some strange battery required although transistor) and my own inverter to sweep the workshop every now and then . I forget what voltage drives it but I remember that if it was set too high it would self discharge internally causing regular clicks . Now there is no thorium loaded gas mantles around these days , nor radium dials , what is commonly around to give an above background check that they are working ? -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://diverse.4mg.com/index.htm |
#7
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Detectron Geiger Counter
In article , "N_Cook" wrote:
Chris F. wrote in message . .. Yes it uses some kind of step-up circuit, and the output to the GM tube is about 300-400 volts. "N_Cook" wrote in message ... Chris F. wrote in message ... I recently bought an old Detectron model DG-7 geiger counter. This is from the early 50's and has three 1U5 tubes inside. Power requirements are 90 volts for the B+, two "D" cells for the tube filaments, and a 4.5 volt bias supply. I went over the unit, replacing a selenium rectifier and testing the tubes. The unit powers up, but generates a steady stream of pulses on it's own, even with the probe detached. The frequency of the oscillation varies with the range selector knob. The probe is working - when brought near a source (a bunch of vaseline marbles) it will produce extra clicks in addition to the stray ones generated by the unit. I've checked all the other components - resistors, capacitors, etc. The only thing I couldn't check is a very small tube, which looks like a cold-cathode rectifier of some kind. I've also tried varying the B+ and bias voltages. And I can't find a schematic, which makes matters worse. I'm not sure what to do next. Any ideas? 90V seems low for a GM, is there a step up circuit to 300V or so ? I use an ex military GM tube with ditched 1960s electronics (some strange battery required although transistor) and my own inverter to sweep the workshop every now and then . I forget what voltage drives it but I remember that if it was set too high it would self discharge internally causing regular clicks . Now there is no thorium loaded gas mantles around these days , nor radium dials , what is commonly around to give an above background check that they are working ? If one has elevated radon levels, there is a rise near your furnace air filter, if its electrostatic material. Still, you have to integrate the meter to see average increases. I still have an old bedside clock around, as well as my Pentax lens, 50mm vintage early 70's. You can buy Uranium stuff. On one meter I use there is a calibration spot on the side. I don't know how many smoke detectors have it, but it seems hard to measure through the case. greg |
#8
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Detectron Geiger Counter
GregS wrote in message
... In article , "N_Cook" wrote: Chris F. wrote in message . .. Yes it uses some kind of step-up circuit, and the output to the GM tube is about 300-400 volts. "N_Cook" wrote in message ... Chris F. wrote in message ... I recently bought an old Detectron model DG-7 geiger counter. This is from the early 50's and has three 1U5 tubes inside. Power requirements are 90 volts for the B+, two "D" cells for the tube filaments, and a 4.5 volt bias supply. I went over the unit, replacing a selenium rectifier and testing the tubes. The unit powers up, but generates a steady stream of pulses on it's own, even with the probe detached. The frequency of the oscillation varies with the range selector knob. The probe is working - when brought near a source (a bunch of vaseline marbles) it will produce extra clicks in addition to the stray ones generated by the unit. I've checked all the other components - resistors, capacitors, etc. The only thing I couldn't check is a very small tube, which looks like a cold-cathode rectifier of some kind. I've also tried varying the B+ and bias voltages. And I can't find a schematic, which makes matters worse. I'm not sure what to do next. Any ideas? 90V seems low for a GM, is there a step up circuit to 300V or so ? I use an ex military GM tube with ditched 1960s electronics (some strange battery required although transistor) and my own inverter to sweep the workshop every now and then . I forget what voltage drives it but I remember that if it was set too high it would self discharge internally causing regular clicks . Now there is no thorium loaded gas mantles around these days , nor radium dials , what is commonly around to give an above background check that they are working ? If one has elevated radon levels, there is a rise near your furnace air filter, if its electrostatic material. Still, you have to integrate the meter to see average increases. I still have an old bedside clock around, as well as my Pentax lens, 50mm vintage early 70's. You can buy Uranium stuff. On one meter I use there is a calibration spot on the side. I don't know how many smoke detectors have it, but it seems hard to measure through the case. greg ordinary domestic smoke detectors use alpha emitters so not much use for GM checking should anyone be unwise to break into the shielding (shielding probably more to keep people out, than the alpha in, as almost anything blocks it) |
#9
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Detectron Geiger Counter
When the b+ becomes to high, the gas-discharge tubes start oscillating, producing a steady stream of pulses. So start with lowering b+ to zero, and then increase, until either back at 90 volts, or the pulses re-appear. At that point lower the voltage a bit, and re-check with your radiation source. Also there should be a capacitor across the tubes somewhere, If so, check their quality(leakage and value). Already tried that, and I replaced all the ceramic capacitors in the circuit. By gas-discharge tube, are you referring to the neon lamp inside? There's another tube, with just two leads, that I can't identify or test. See this photo: http://s282.photobucket.com/albums/k...=detectron.jpg |
#10
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Detectron Geiger Counter
Schematic of the DG-9 model: http://www.curtcass.com/detectron/dg9-sch.jpg Probably quite similar to the DG-7. I came across that already, but it's quite different and therefore not much help. Replace it with what? Is silicon, the B+ is probably too high. I tried putting a decade resistor in series with the diode, but even at 100k-ohms it still didn't make a difference. It still oscillates even with the diode disconnected. and testing the tubes. How? With a tube tester? I sometimes work on ancient Motorola radios with pencil tubes. I have to make my own adapter to work in the tube tester. Yes, I checked these with a tube tester, and even trying subbing them with new-old-stock tubes. Nope. Probably a neon lamp used as a regulator. Photo? Here's a photo of the circuit: http://s282.photobucket.com/albums/k...=detectron.jpg |
#11
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Detectron Geiger Counter
Chris F. wrote:
When the b+ becomes to high, the gas-discharge tubes start oscillating, producing a steady stream of pulses. So start with lowering b+ to zero, and then increase, until either back at 90 volts, or the pulses re-appear. At that point lower the voltage a bit, and re-check with your radiation source. Also there should be a capacitor across the tubes somewhere, If so, check their quality(leakage and value). Already tried that, and I replaced all the ceramic capacitors in the circuit. By gas-discharge tube, are you referring to the neon lamp inside? There's another tube, with just two leads, that I can't identify or test. See this photo: http://s282.photobucket.com/albums/k...=detectron.jpg No, I was referring to a detector tube filled with neon, where the voltage on the tube is just below the sustained ignition level, and where the charged particle causes a conducting ion trail, which discharges the parallel capacitor a little bit, causing the click signal you can pick off. The feed resistor slowly restores the voltage accross the tube/cap. The amplitude of the click shows the energy level of the detected particle. Long ago I built a cosmic ray detector/display using these tubes. Name is geiger muller tube I think. |
#12
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Detectron Geiger Counter
No, I was referring to a detector tube filled with neon, where the voltage on the tube is just below the sustained ignition level, and where the charged particle causes a conducting ion trail, which discharges the parallel capacitor a little bit, causing the click signal you can pick off. The feed resistor slowly restores the voltage accross the tube/cap. The amplitude of the click shows the energy level of the detected particle. Long ago I built a cosmic ray detector/display using these tubes. Name is geiger muller tube I think. OK I understand. But that's still not the problem, because the unit produces its own clicks whether the probe is connected or not........ |
#13
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Detectron Geiger Counter
On Fri, 23 Apr 2010 10:38:23 -0700, "Chris F."
wrote: Schematic of the DG-9 model: http://www.curtcass.com/detectron/dg9-sch.jpg Probably quite similar to the DG-7. I came across that already, but it's quite different and therefore not much help. Oh, I was hoping they were similar. Sorry(tm). Replace it with what? Is silicon, the B+ is probably too high. I tried putting a decade resistor in series with the diode, but even at 100k-ohms it still didn't make a difference. It still oscillates even with the diode disconnected. I don't know exactly what series resistor is going to work. 100K is certainly too large. When I was doing the same thing on much higher power ancient Motorola radios, about 10 ohms 25 watts was about right. I'll probably get yelled at for this suggestion, but use an ohmmeter to mearsure the selenium recifiers forward resistance and use a resistor with a slightly lower value. I dug around with Google and found recommendations varying from 30 to 90 ohms for low power devices. http://wiki.answers.com/Q/Can_you_replace_a_selenium_rectifier_with_a_silico n_rectifier Yes, I checked these with a tube tester, and even trying subbing them with new-old-stock tubes. The tubes are probably fine since it does go click on your vasalene marbles. Here's a photo of the circuit: http://s282.photobucket.com/albums/k...=detectron.jpg Yech. Note the big paper electrolytic cazapitor. I can't tell if it's a power supply filter cap or across the meter to smooth the output. If across the power supply, replace it as judging by the age and type, it's almost certainly dead. If you have an ESR tester, use it. (If you don't have one, buy or build one). I'll stand on my comments that your clip lead and external power supply kludge is probably causing problems. Find some suitable electrolytics and place them across where the battery would normally connect. The idea is to reduce the impedance that the counter sees in the direction of the power supplies. That should reduce the motorboating (oscillation). -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com # http://www.LearnByDestroying.com AE6KS |
#14
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Detectron Geiger Counter
Jeff Liebermann wrote in message ... On Fri, 23 Apr 2010 10:38:23 -0700, "Chris F." wrote: Schematic of the DG-9 model: http://www.curtcass.com/detectron/dg9-sch.jpg Probably quite similar to the DG-7. I'll stand on my comments that your clip lead and external power supply kludge is probably causing problems. Find some suitable electrolytics and place them across where the battery would normally connect. The idea is to reduce the impedance that the counter sees in the direction of the power supplies. That should reduce the motorboating (oscillation). -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com # http://www.LearnByDestroying.com AE6KS Does USA "kludge" = UK "bodge" ? |
#15
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Detectron Geiger Counter
On Sat, 24 Apr 2010 09:02:32 +0100, "N_Cook"
wrote: Jeff Liebermann wrote in message .. . On Fri, 23 Apr 2010 10:38:23 -0700, "Chris F." wrote: Schematic of the DG-9 model: http://www.curtcass.com/detectron/dg9-sch.jpg Probably quite similar to the DG-7. I'll stand on my comments that your clip lead and external power supply kludge is probably causing problems. Find some suitable electrolytics and place them across where the battery would normally connect. The idea is to reduce the impedance that the counter sees in the direction of the power supplies. That should reduce the motorboating (oscillation). -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com # http://www.LearnByDestroying.com AE6KS Does USA "kludge" = UK "bodge" ? Yes... |
#16
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Detectron Geiger Counter
I'll stand on my comments that your clip lead and external power supply kludge is probably causing problems. Find some suitable electrolytics and place them across where the battery would normally connect. The idea is to reduce the impedance that the counter sees in the direction of the power supplies. That should reduce the motorboating (oscillation). I tried putting a 100uF cap in that area, the result was that it greatly increased the frequency of the stray clicks.... I wonder if a row of 10 9-volt batteries would work? |
#17
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Detectron Geiger Counter
On Sat, 24 Apr 2010 07:51:13 -0700, "Chris F."
wrote: I'll stand on my comments that your clip lead and external power supply kludge is probably causing problems. Find some suitable electrolytics and place them across where the battery would normally connect. The idea is to reduce the impedance that the counter sees in the direction of the power supplies. That should reduce the motorboating (oscillation). I tried putting a 100uF cap in that area, the result was that it greatly increased the frequency of the stray clicks.... Did you figure out where the yellow electrolytic in the photo was connected? Power supply filter or meter integrator? Find an oscilloscope that can tolerate some high voltage (i.e. 100x probe). Look at the power supply line. Got pulses? If so, get rid of them with a filter cap. Old carbon composition resistors tend to change value with age (and moisture). With the power off, you might walk though the pile and see if there are any that are radically off value. I don't think this is causing the problem, but it might be contributory. I wonder if a row of 10 9-volt batteries would work? Probably, but rather expensive. It should work with your external power supplies, but due to the apparent lack of power supply filtering, it might be oscillating. If all else fails, trace out the schematic. It doesn't look all that messy and you can probably use the DG-9 schematic as a guide. The author of the web site where we found the DG-9 schematic is the founders son. Send him email asking if he has a DG-7 schematic or if he knowns anyone that can help. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#18
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Detectron Geiger Counter
On Sat, 24 Apr 2010 09:02:32 +0100, "N_Cook"
wrote: Does USA "kludge" = UK "bodge" ? I think so. Also sometimes spelled kluge. http://en.wikipedia.org/wiki/Kludge -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#19
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Detectron Geiger Counter
Did you figure out where the yellow electrolytic in the photo was
connected? Power supply filter or meter integrator? It's connected across the meter. Find an oscilloscope that can tolerate some high voltage (i.e. 100x probe). Look at the power supply line. Got pulses? If so, get rid of them with a filter cap. Already tried that.... or are you talking about the AC line feeding my transformer/rectifier/cap power supply? Old carbon composition resistors tend to change value with age (and moisture). With the power off, you might walk though the pile and see if there are any that are radically off value. I don't think this is causing the problem, but it might be contributory. Checked them all, and all are well within their specified tolerances. I wonder if a row of 10 9-volt batteries would work? Probably, but rather expensive. It should work with your external power supplies, but due to the apparent lack of power supply filtering, it might be oscillating. If all else fails, trace out the schematic. It doesn't look all that messy and you can probably use the DG-9 schematic as a guide. The author of the web site where we found the DG-9 schematic is the founders son. Send him email asking if he has a DG-7 schematic or if he knowns anyone that can help. I might do that. Can't think of anything else it might be, as it's really a rather basic circuit. BTW that small tube with the 2 leads I mentioned is a 5841 (voltage regulator), and I don't have a sub for it. |
#20
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Detectron Geiger Counter
"Chris F." wrote in message ... If all else fails, trace out the schematic. It doesn't look all that messy and you can probably use the DG-9 schematic as a guide. The author of the web site where we found the DG-9 schematic is the founders son. Send him email asking if he has a DG-7 schematic or if he knowns anyone that can help. I might do that. Can't think of anything else it might be, as it's really a rather basic circuit. BTW that small tube with the 2 leads I mentioned is a 5841 (voltage regulator), and I don't have a sub for it. Check this out: http://www.dvq.com/geiger/heath_rc1.pdf Googleing says it is a 900 volt regulator. maybe a stack of 150 volt zeners would work. I did see some replacements available. |
#21
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Detectron Geiger Counter
On 4/24/2010 1:02 AM N_Cook spake thus:
Jeff Liebermann wrote in message ... On Fri, 23 Apr 2010 10:38:23 -0700, "Chris F." wrote: Schematic of the DG-9 model: http://www.curtcass.com/detectron/dg9-sch.jpg Probably quite similar to the DG-7. I'll stand on my comments that your clip lead and external power supply kludge is probably causing problems. Find some suitable electrolytics and place them across where the battery would normally connect. The idea is to reduce the impedance that the counter sees in the direction of the power supplies. That should reduce the motorboating (oscillation). Does USA "kludge" = UK "bodge" ? Yes, except that I'm going to insist that the proper spelling is "kluge"[1], which rhymes with "luge", not kludge which would rhyme with fudge (which would just be wrong!). [1] I'm fairly certain, though I can't prove it, that this term comes from a line of printing equipment made by the company called Kluge, which included a number of very complex Rube-Goldbergian machines, hence the current usage. -- The fashion in killing has an insouciant, flirty style this spring, with the flaunting of well-defined muscle, wrapped in flags. - Comment from an article on Antiwar.com (http://antiwar.com) |
#22
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Detectron Geiger Counter
On Sat, 24 Apr 2010 07:51:13 -0700, "Chris F."
wrote: I'll stand on my comments that your clip lead and external power supply kludge is probably causing problems. Find some suitable electrolytics and place them across where the battery would normally connect. The idea is to reduce the impedance that the counter sees in the direction of the power supplies. That should reduce the motorboating (oscillation). I tried putting a 100uF cap in that area, the result was that it greatly increased the frequency of the stray clicks.... I wonder if a row of 10 9-volt batteries would work? Probably would, but may not for very long. Why not an inverter with an output of about 90 VDC? The current is not very great, you could probalby bodge one together easily enough. |
#23
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Detectron Geiger Counter
On Fri, 23 Apr 2010 16:00:06 +0100, "N_Cook"
wrote: Now there is no thorium loaded gas mantles around these days Ummm... check out the gas and kerosene mantles from China. Some are hot: http://www.tradevv.com/chinasuppliers/yansong_p_4e599/china-Gas-mantle.html Incidentally, I once sacrificed one of my radioactive thorium Coleman lantern mantles and ran a side by side comparison of the brightness with a current non-radioactive zirconium mantle. The radioactive mantle was MUCH brighter. nor radium dials , what is commonly around to give an above background check that they are working ? I like to use KCL (potassium salt, lite salt, or low-sodium salt). The Potassium 40 is radioactive (450pCi/gram): http://802.11junk.com/jeffl/crud/salt.jpg http://www.angelfire.com/electronic/cwillis/rad/nosalt.html It's not very hot but works well enough with a GM tube. Also lots of fun going to the market with my 1950's GM counter. I once found some brand of sea salt that was really hot, but it had been withdrawn or recalled before I could return to buy some. While at the market, try brazil nuts, acorns, and bananas. K-40 but only when grown with massive overkill doses of fertilizer. Also try cat litter. They all show up hot with my scintillation counter, but are very weak with the GM tube. If you go to the hardware store, check out the high phosphate fertilizer. The stuff has uranium, K-40, thorium, radium, and who know what else in it. While at the hardware store, see if they have any tungsten stick arc electrodes. They have some Thorium mixed in. At home, if you have a dark colored granite counter top, you'll find it somewhat radioactive from uranium. http://greenbuildingelements.com/2009/03/27/granite-showrooms-continue-selling-radioactive-granite/ The problem isn't so much the radiation. It's the radon gas that it produces. Got any pottery or kitchen plates with a yellow or bright orange glaze (Fiestaware)? If so, they're uranium oxide. Got any old cameras or eyeglasses made between WWII and about 1980? Most lenses have thorium mixed into the glass to increase the index of refraction. These are really weak and will only show up on my scintillation counter. Got a heavy scotch tape dispenser with a sand-epoxy mix in the base? The sand has thorium mixed in. Got an old static eliminator for removing the static electricity from old vinyl records? If so, it's quite hot with Polonium. Mo http://www.kronjaeger.com/hv-old/radio/src/index.html http://www.anythingradioactive.com/radsamples.htm http://www.physics.isu.edu/radinf/natural.htm See section on food. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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Detectron Geiger Counter
In message , Jeff Liebermann
writes On Sat, 24 Apr 2010 09:02:32 +0100, "N_Cook" wrote: Does USA "kludge" = UK "bodge" ? I think so. Also sometimes spelled kluge. http://en.wikipedia.org/wiki/Kludge Be aware that, while "bodge" and "botch" tend to get used interchangeably, "bodging" and "botching" are not the same thing. A "bodger" is a skilled, itinerant wood worker. http://en.wikipedia.org/wiki/Bodging A "botcher" is someone who fakes doing a proper job of something. If a kludge provides a functionally adequate (but inelegant) solution, I'm not sure whether it is really a bodge or a botch. -- Ian |
#25
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Detectron Geiger Counter
On Sun, 25 Apr 2010 08:53:38 +0100, Ian Jackson
wrote: In message , Jeff Liebermann writes On Sat, 24 Apr 2010 09:02:32 +0100, "N_Cook" wrote: Does USA "kludge" = UK "bodge" ? I think so. Also sometimes spelled kluge. http://en.wikipedia.org/wiki/Kludge Be aware that, while "bodge" and "botch" tend to get used interchangeably, "bodging" and "botching" are not the same thing. A "bodger" is a skilled, itinerant wood worker. http://en.wikipedia.org/wiki/Bodging A "botcher" is someone who fakes doing a proper job of something. If a kludge provides a functionally adequate (but inelegant) solution, I'm not sure whether it is really a bodge or a botch. Ok, I'm lost in the translation. However, it's good to know that the Kings English has multiple names for what I do naturally when confronted with a technical problem. Such multiple names are a sign of sophistication and tends to identify what a society considers important. For example, the Eskimo's have multiple names for different types of snow. In Yiddish, we have multiple names for the different types of "idiot". In government, there are multiple names for the different types of taxation. I'm sure something profound can be extracted from all this, but I don't want to ruin a nice weekend by attempting to think. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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Detectron Geiger Counter
Chris F. Inscribed thus:
At this point, I think you're right - it's probably issue with the B+ supply, probably a combination of poor filtering and inadequate output current. After tracing out the schematic that's about the only conclusion I can come to. Since you get clicks when the tube is not connected, have you checked the EHT supply. It probably has bad caps in there. Something breaking down as the EHT rises. -- Best Regards: Baron. |
#27
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Detectron Geiger Counter
Jeff Liebermann Inscribed thus:
On Fri, 23 Apr 2010 16:00:06 +0100, "N_Cook" wrote: Now there is no thorium loaded gas mantles around these days Ummm... check out the gas and kerosene mantles from China. Some are hot: http://www.tradevv.com/chinasuppliers/yansong_p_4e599/china-Gas-mantle.html Incidentally, I once sacrificed one of my radioactive thorium Coleman lantern mantles and ran a side by side comparison of the brightness with a current non-radioactive zirconium mantle. The radioactive mantle was MUCH brighter. nor radium dials , what is commonly around to give an above background check that they are working ? I like to use KCL (potassium salt, lite salt, or low-sodium salt). The Potassium 40 is radioactive (450pCi/gram): http://802.11junk.com/jeffl/crud/salt.jpg http://www.angelfire.com/electronic/cwillis/rad/nosalt.html It's not very hot but works well enough with a GM tube. Also lots of fun going to the market with my 1950's GM counter. I once found some brand of sea salt that was really hot, but it had been withdrawn or recalled before I could return to buy some. While at the market, try brazil nuts, acorns, and bananas. K-40 but only when grown with massive overkill doses of fertilizer. Also try cat litter. They all show up hot with my scintillation counter, but are very weak with the GM tube. If you go to the hardware store, check out the high phosphate fertilizer. The stuff has uranium, K-40, thorium, radium, and who know what else in it. While at the hardware store, see if they have any tungsten stick arc electrodes. They have some Thorium mixed in. At home, if you have a dark colored granite counter top, you'll find it somewhat radioactive from uranium. http://greenbuildingelements.com/2009/03/27/granite-showrooms-continue-selling-radioactive-granite/ The problem isn't so much the radiation. It's the radon gas that it produces. Got any pottery or kitchen plates with a yellow or bright orange glaze (Fiestaware)? If so, they're uranium oxide. Got any old cameras or eyeglasses made between WWII and about 1980? Most lenses have thorium mixed into the glass to increase the index of refraction. These are really weak and will only show up on my scintillation counter. Got a heavy scotch tape dispenser with a sand-epoxy mix in the base? The sand has thorium mixed in. Got an old static eliminator for removing the static electricity from old vinyl records? If so, it's quite hot with Polonium. Mo http://www.kronjaeger.com/hv-old/radio/src/index.html http://www.anythingradioactive.com/radsamples.htm http://www.physics.isu.edu/radinf/natural.htm See section on food. Hey Jeff, I've several old valves (Tubes) that are marked as containing "Radio Active Material" with a "Do not Break Glass" and a yellow sticker on them. CV number marking. Any ideas ? They are stored in a box somewhere. If I can find them I'll come back with the CV numbers. -- Best Regards: Baron. |
#28
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Detectron Geiger Counter
Actually, the way this circuit is designed, any ripple or pulses in the DC
supply will be picked up and amplified the same way as pulses from the GM tube. I guess it was never designed to operate on an AC power supply, but I'm sure there's some way areound the problem. I've replaced most of the capacitors (all are high voltage ceramics). "Baron" wrote in message ... Chris F. Inscribed thus: At this point, I think you're right - it's probably issue with the B+ supply, probably a combination of poor filtering and inadequate output current. After tracing out the schematic that's about the only conclusion I can come to. Since you get clicks when the tube is not connected, have you checked the EHT supply. It probably has bad caps in there. Something breaking down as the EHT rises. -- Best Regards: Baron. |
#29
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Detectron Geiger Counter
Hey Jeff, I've several old valves (Tubes) that are marked as containing "Radio Active Material" with a "Do not Break Glass" and a yellow sticker on them. CV number marking. Any ideas ? They are stored in a box somewhere. If I can find them I'll come back with the CV numbers. -- Best Regards: Baron. Probably cold-cathode rectifier tubes, equivalent to types like 0A2, 0D3, etc. I have at least one American-made 0A2 that has a radioactive symbol on the box, and the tube itself says "Contains less than 0.03 microcuries of Krypton". |
#30
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Detectron Geiger Counter
Chris F. Inscribed thus:
Actually, the way this circuit is designed, any ripple or pulses in the DC supply will be picked up and amplified the same way as pulses from the GM tube. I guess it was never designed to operate on an AC power supply, but I'm sure there's some way areound the problem. I've replaced most of the capacitors (all are high voltage ceramics). Sods Law ! It will be the one that you didn't replace. :-) -- Best Regards: Baron. |
#31
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Detectron Geiger Counter
Did you read the information in this link? Scroll down to the
discussion on the regulator tube. http://www.dvq.com/geiger/heath_rc1.pdf The 900 volt regulator tube operates in three regions; corona, glow, and arc. It is sensitive to the high voltage supply conditions, i.e. ripple can cause it to oscillate between the modes. Also, it is sensitive to the filter capacitance. |
#32
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Detectron Geiger Counter
On Sun, 25 Apr 2010 17:28:31 +0100, Baron
wrote: Hey Jeff, You rang? I've several old valves (Tubes) that are marked as containing "Radio Active Material" with a "Do not Break Glass" and a yellow sticker on them. CV number marking. Any ideas ? Tubes are what you roll the toilet paper upon. Valves are what controls the flushing. What more do you need to know? They are stored in a box somewhere. If I can find them I'll come back with the CV numbers. My guess(tm) is a gas filled thyratron or regulator tube/valve/whatever, where the gas is slightly radioactive to decrease the ionization voltage. The cathodes were also made with thorium: http://www.angelfire.com/electronic/cwillis/rad/tubes.html http://www.tubecollector.org/documents/radioactive.htm The 5841 voltage regulator is one of those that is filled with some radioactive gas. The differences between the various versions, which breakdown at different voltages, is the amount and type of radioactive gas or material. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#33
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Detectron Geiger Counter
I finally got this working, at least to the point where it's now usable. The
trick was to filter the B+ supply between the three tubes, with a filter+inductor+filter combination, to prevent stray oscillation. It still generates about 1 stray pulse every 5 seconds or so (not counting normal background readings), but this may straighten out with some tweaking. Even if not, the detector is now suitable for measuring above-background levels of radiation, up to about 20 mr/hr. Should come in handy if the nearby nuclear power plant ever blows.... Thanks to all for the advice. "Chris F." wrote in message ... I recently bought an old Detectron model DG-7 geiger counter. This is from the early 50's and has three 1U5 tubes inside. Power requirements are 90 volts for the B+, two "D" cells for the tube filaments, and a 4.5 volt bias supply. I went over the unit, replacing a selenium rectifier and testing the tubes. The unit powers up, but generates a steady stream of pulses on it's own, even with the probe detached. The frequency of the oscillation varies with the range selector knob. The probe is working - when brought near a source (a bunch of vaseline marbles) it will produce extra clicks in addition to the stray ones generated by the unit. I've checked all the other components - resistors, capacitors, etc. The only thing I couldn't check is a very small tube, which looks like a cold-cathode rectifier of some kind. I've also tried varying the B+ and bias voltages. And I can't find a schematic, which makes matters worse. I'm not sure what to do next. Any ideas? |
#34
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Detectron Geiger Counter
Chris F. wrote in message
... I finally got this working, at least to the point where it's now usable. The trick was to filter the B+ supply between the three tubes, with a filter+inductor+filter combination, to prevent stray oscillation. It still generates about 1 stray pulse every 5 seconds or so (not counting normal background readings), but this may straighten out with some tweaking. Even if not, the detector is now suitable for measuring above-background levels of radiation, up to about 20 mr/hr. Should come in handy if the nearby nuclear power plant ever blows.... Thanks to all for the advice. "Chris F." wrote in message ... I recently bought an old Detectron model DG-7 geiger counter. This is from the early 50's and has three 1U5 tubes inside. Power requirements are 90 volts for the B+, two "D" cells for the tube filaments, and a 4.5 volt bias supply. I went over the unit, replacing a selenium rectifier and testing the tubes. The unit powers up, but generates a steady stream of pulses on it's own, even with the probe detached. The frequency of the oscillation varies with the range selector knob. The probe is working - when brought near a source (a bunch of vaseline marbles) it will produce extra clicks in addition to the stray ones generated by the unit. I've checked all the other components - resistors, capacitors, etc. The only thing I couldn't check is a very small tube, which looks like a cold-cathode rectifier of some kind. I've also tried varying the B+ and bias voltages. And I can't find a schematic, which makes matters worse. I'm not sure what to do next. Any ideas? So what have you found for a long-term test source , high enough emitter at a repeatable distance, to say give a count at least 5 times more than background? I've managed to lose my old broken gas-lighting mantle I had retained for this purpose |
#35
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Detectron Geiger Counter
Chris F. wrote:
Should come in handy if the nearby nuclear power plant ever blows.... Homer Simpson laughing at the "Run for the hills" alert level on the warning sign at the power plant. "That will never happen." Lenny asks him if he thought the power plant was safe. "No, if the plant blows up, there won't be any electricity to power the sign." Jeff -- “Egotism is the anesthetic that dulls the pain of stupidity.” Frank Leahy, Head coach, Notre Dame 1941-1954 http://www.stay-connect.com |
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