Detectron Geiger Counter
Chris F.
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?
Sjouke Burry
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).
Jeff Liebermann
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 je...@cruzio.com
# http://www.LearnByDestroying.com AE6KS
N_Cook
news:4bd08a44$0$12419$9a56...@news.aliant.net...
90V seems low for a GM, is there a step up circuit to 300V or so ?
Chris F.
about 300-400 volts.
"N_Cook" <div...@tcp.co.uk> wrote in message
news:hqrj97$20q$4...@news.eternal-september.org...
N_Cook
I use an ex military GM tube with ditched 1960s electronics (some strange
battery required although transistor) and my own inverter to sweep the
workshop every now and then . I forget what voltage drives it but I remember
that if it was set too high it would self discharge internally causing
regular clicks .
Now there is no thorium loaded gas mantles around these days , nor radium
dials , what is commonly around to give an above background check that they
are working ?
--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://diverse.4mg.com/index.htm
GregS
If one has elevated radon levels, there is a rise near your furnace air filter,
if its electrostatic material. Still, you have to integrate the meter to see
average increases. I still have an old bedside clock around, as well
as my Pentax lens, 50mm vintage early 70's. You can buy Uranium stuff.
On one meter I use there is a calibration spot on the side. I don't know how many smoke detectors
have it, but it seems hard to measure through the case.
greg
N_Cook
news:hqsd6m$mqd$1...@usenet01.srv.cis.pitt.edu...
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)
Chris F.
>>
> 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/kk275/packrat79/?action=view¤t=detectron.jpg
Chris F.
> 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/kk275/packrat79/?action=view¤t=detectron.jpg
Sjouke Burry
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.
Chris F.
> 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........
Jeff Liebermann
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_silicon_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/kk275/packrat79/?action=view¤t=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).
N_Cook
Jeff Liebermann <je...@cruzio.com> wrote in message
news:kcf4t5hlkdkjj4h04...@4ax.com...
> On Fri, 23 Apr 2010 10:38:23 -0700, "Chris F." <zapp...@hotmail.com>
> 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 je...@cruzio.com
> # http://www.LearnByDestroying.com AE6KS
Does USA "kludge" = UK "bodge" ?
PeterD
Chris F.
> 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?
Jeff Liebermann
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 je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Jeff Liebermann
wrote:
>Does USA "kludge" = UK "bodge" ?
I think so. Also sometimes spelled kluge.
<http://en.wikipedia.org/wiki/Kludge>
Chris F.
> 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.
tm
>
>>
>>
>>
>> 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.
David Nebenzahl
> Jeff Liebermann <je...@cruzio.com> wrote in message
> news:kcf4t5hlkdkjj4h04...@4ax.com...
>
>> On Fri, 23 Apr 2010 10:38:23 -0700, "Chris F." <zapp...@hotmail.com>
>> 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)
PeterD
wrote:
>
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.
Jeff Liebermann
wrote:
>> 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.
Ok, ignore it. I was hopeing for power supply.
>> 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?
No. I meant high voltage battery positive lead. If there's
motorboating there, then the power supply may need to be filtered.
If that shows nothing useful, follow the signal path from the GM tube
(after the coupling capacitor so that you're not looking at 900VDC) to
the first grid, to that tube's plate, to the next grid, and so on. You
should be able to see the motorboating.
>I might do that. Can't think of anything else it might be, as it's really a
>rather basic circuit.
Then, trace it out. From the photo, it looks simple enough.
>BTW that small tube with the 2 leads I mentioned is a
>5841 (voltage regulator), and I don't have a sub for it.
It's a 900VDC regulator. Same as Victoreen GV3A-900.
<http://www.logwell.com/tech/app_notes/VictoreenCatalog.pdf>
See if there's any oscillations cross the tube with a high-voltage
probe. It could be acting as a relaxation oscillator (as in a
neon-lamp oscillator). Solid state replacement:
<http://www.logwell.com/products/Codatron_Corotron.html>
More for the collection (but nothing useful):
<http://www.orau.org/ptp/collection/surveymeters/Detectrondg7.htm>
<http://www.nukeworker.com/pictures/displayimage-442-47.html>
<http://www.orau.org/ptp/collection/surveymeters/Detectrondg2.htm>
<http://www.dvq.com/geiger/detdg7.jpg>
<http://www.vex.net/~flint/geigerboy/page3.htm>
Here's an eBay listing that has expired.
<http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=270535217184>
Jeff Liebermann
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.
More:
<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.
Ian Jackson
<je...@cruzio.com> writes
>On Sat, 24 Apr 2010 09:02:32 +0100, "N_Cook" <div...@tcp.co.uk>
>wrote:
>
>>Does USA "kludge" = UK "bodge" ?
>
>I think so. Also sometimes spelled kluge.
><http://en.wikipedia.org/wiki/Kludge>
>
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
Chris F.
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. I'm going to take a break from this for a while, and then try
building a better power supply, and I will post back with the results.
There was something of interest in those links you posted; one specified a
15-volt C battery (for the tube bias) - I was only using about 4.5V. Don't
know if that would have much effect on things, but it's worth a try.
Thanks for the advice.
"Jeff Liebermann" <je...@cruzio.com> wrote in message
news:6a37t5hbf22hf1dum...@4ax.com...
Jeff Liebermann
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.
Baron
> 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.
Baron
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.
Chris F.
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" <baron....@linuxmaniac.nospam.net> wrote in message
news:hr1pta$uog$1...@news.eternal-september.org...
Chris F.
> 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".
Baron
> 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.
tm
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.
Jeff Liebermann
<baron....@linuxmaniac.nospam.net> 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.
Chris F.
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.news:4bd08a44$0$12419$9a56...@news.aliant.net...
> 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?
>
N_Cook
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
Jeffrey D Angus
> 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