INSTALLATION AND USE OF THE 1B85 REPLACEMENT GEIGER TUBE AND OTHER HINTS ON RESTORING YOUR GEIGER COUNTER DESCRIPTION The Replacement for the 1B85 Geiger tube is constructed to look like the 1B85, and fits Geiger counters that use the 1B85. COMPARATIVE OPERATIONAL CHARACTERISTICS The 1B85 is a 900 volt organically-quenched thinwall Geiger tube, sensitive to Beta particles and gamma rays. The replacement 1B85 uses a Raytheon CK1026 halogen-quenched glass Geiger tube with similar characteristics. This tube is encased in a very thin (0.003") aluminum sleeve; the sleeve density is about 18mg/sq-cm, and has little effect on beta particles, and virtually no effect on the more penetrating gamma rays. The active length for the 1B85 is about three inches; the replacement 1B85, about two inches. Tests conducted in several counters (Detectron DG-7, Detectron DG-2, PRI 106B, PRI 107B) show that the effective sensitivity is nearly the same. Calibration with a 1 mR/Hr Gamma source (Cs-137) shows no measurable difference. The 1B85 has a life limited to about 10E8 counts, as it is an organically-quenched tube. The life of the CK1026 is essentially unlimited, as it is halogen-quenched. Operational and storage temperature and humidity: -10 deg. F to +120 deg. F, 95% RH. WHAT’S IN THIS KIT: 1. One Raytheon CK1026 Geiger tube inside the 1B85 look-alike skin. 2. One "O" ring 3. One piece of foam rubber 4. These instructions INSTALLATION CAUTION: the envelope of the 1B85 Replacement is VERY THIN. Do not squeeze or twist it! 1. Make sure the counter is OFF. (The 900 volts probably won’t hurt you, but it can be a nasty surprise!) 2. Open the counter, or the probe to expose the old 1B85. 3. If the tube is in a probe, look for a seam around the probe. Chances are that the probe unscrews at that point. Some probes have screws placed radially near a seam. You’ll find the tube is probably plugged into a socket, or, as in the PRI 107B, in a spring clip and tube cap connector. Simply wiggle, twist slightly, and pull it out. Place the replacement in the socket, or carefully replace the spring clip and connector, and reassemble the probe. DON’T SQUEEZE THE TUBE! 4. If the tube is inside the counter, you may encounter several mounting schemes; typical is a snap-ring that holds the 1B85 in a plastic insulator. Use only the proper snap-ring tool (available at good auto parts stores) to remove it, as it is very tight. Take your time; the plastic is old, and cracks easily. Remove the center pin connector (it pulls off). The old tube is now removable. Other mounting schemes include various clips, spiral wires, etc. Remove carefully to extract the old tube. 5. To install the replacement 1B85 in a holder that uses a snap-ring, hold the tube’s flange against its mount with your fingernails, and use the snap-ring tool. The snap-ring is so tight that trying to assemble without the tool will almost certainly result in destruction of the replacement 1B85, as the forces are very high, and the operation very difficult. Remember, the warranty on the replacement 1B85 does not cover crumpled tubes!! 6. Wire type holders will generally be easier to assemble than the snap-ring type, but take your time, and be careful! 7. Be sure to replace the connection to the center pin of the replacement. While you slip this connection on, you can hold the 1B85 replacement tube at the base flange with your fingernails. Don’t squeeze the tube, and don’t press on it from the opposite end!! 8. NOTE: Some counters have the outside of the Geiger tube insulated by a plastic mount or thin plastic sheath (probe type). Make sure the shell of the tube does not touch the frame of the counter or metal of the probe. If it looks like it could short, gently wrap a piece of the supplied foam around the end of the tube to keep it from touching anything. 9. Install the batteries (see below for battery ideas) and put the counter and/or probe back together. TESTING 1. Turn the counter ON, and set to the most sensitive scale (usually 0.2 mR/Hr). You should hear clicks from the headphone, and see the meter ‘kick’ ever so often (30 to 40 counts per minute is normal for background count from cosmic rays). CAUTION: if the meter needle swings wildly over to maximum, and/or a raspy hiss is heard from the headphone, turn the counter off immediately. Please refer to the troubleshooting section below. If it appears to work ok, continue with step 2. 2. If you have a radium-dial watch or clock, or a bright orange "Fiestaware" dish, or a piece of "vaseline" Uranium glassware (it’s a clear yellow-green, about the color of lemon-lime Koolaid), bring it close to the counter tube; you’ll see the meter needle swing upscale, and hear lots of clicks from the headphone. Your counter is working! Enjoy! NOTE: all radioactive materials are potentially dangerous. Refer to sites on the Internet for proper methods of handling radioactive items. 3. If you have a calibration standard, you can check calibration, and, if the counter has a calibrate control, calibrate the counter. If there is no calibration control, simply move the calibration standard to a distance that gives the proper reading, and remember to use that distance when you are checking minerals. TROUBLESHOOTING NOTE: Some of these procedures are easy for non-electronic people; some require a fair understanding of electronics, and some require the schematic and a very specific background in GM counter electronics. The average TV serviceman, well-meaning as he may be, may not be able to help much. The following is an attempt to help you service it yourself with minimal electronic knowledge and tools. There are a few things that commonly happen to the older counters that can cause trouble: 1. The most likely problem is that a battery holder is corroded and is not making contact. Be sure to clean any corrosion off with fine sandpaper. Do that cleaning first. It saves a lot of troubleshooting time later! If the holder is past redemption, a good selection of new holders are available from Mouser. See suppliers section below. 2. The second most likely problem is a high voltage capacitor is ‘leaky’ (its insulation has degraded over time). Symptoms are that the counter won’t count, but you will [probably] hear a slight ‘buzz’ from the circuit area (that’s the high voltage power supply trying to work). Look for a cylinder, about 3/8 to 5/8 inch diameter, about 1-1/4 to 1-1/2 inch long, with a wire coming out of each end. There may be more than one Look for markings that say, ".0047 MF 1000 VDC", or similar. It might be "1600VDC", and/or ".005 MF", or ".01 MF". It may have no writing, but rather it may be a [usually black] plastic cylinder with colored bands around it. That capacitor is likely to be leaky. You can obtain replacements from one of the parts sources listed below. The replacement won’t look exactly like the original (it may look like a brown disk with wires). If you don’t want to solder it in, simply remove the old one, clipping its leads close to the capacitor’s body; then twist the wires of the new one onto the stubs of the old one, and clip off the excess (a nail clippers will work). Position the new capacitor so its wires are at least 1/8 inch from any other [bare] terminal or wire. If it might flop around, fasten it down with epoxy or glue If you find more than one of these type of capacitors, replace them all (usually only two are used, so it’s not all that big a job). The ‘type’ of replacement capacitor is relatively unimportant; a "ceramic" is shaped like a disk, with a wire coming off of each side; the wrap-and-fill type is cylindrical, similar to the original, but usually with radial leads, rather than axial. Also the exact value [in MF] (or "uF", to use the newer terminology) is not important in this circuit a .0047 can be replaced with a .0033 through .01 with no detectable change in performance, in most cases. Nor is the voltage rating critical but always opt for a higher-voltage replacement, if you have a choice. 3. The third most likely problem is that a wire has broken. The average 1950’s GM counter is a maze of loose wiring, and it gets snagged rather easily. Symptoms can be no [high voltage generator] buzz, no counting, meter reads full scale all the time, intermittent operation, etc. First use your eyes; you don’t have to know any electronics, just look for a wire that "ends in mid-air". Don’t move stuff around just yet; the reason is that it is MUCH easier to find where the [broken] wire goes if you don’t move it unnecessarily. If you don’t see anything, try using a toothpick to carefully push on wires Don’t use a pencil the ‘lead’ (it’s really graphite) is conductive, and marks you might leave are conductive, and could compound your problem! When you find the ‘culprit’, observe very carefully all the terminals (connection points) in the area; one will have a very short stub of wire sticking out of the solder. The tips of this stub generally show a copper color. Strip the wire, and neatly solder it back onto the terminal. Your local TV shop can solder it on if you don’t have a soldering iron. 4. The fourth most common problem is failure of a vacuum tube. There may be one or more tubes. If they are in sockets, then it is easy to test them, and that should be done first. Care! Make a little diagram of which tube goes where!! Replace any very weak or dead tubes and try the counter again. Common tubes are 1T4, 1U4, 1U5, 1AF4, 3A5. They are not expensive; check the source list below. By the way, if you find ALL of the tubes are dead, it is likely that one of two things happened: 1) a tube shorted, and blew all the other tube’s filaments, or 2) someone installed a battery wrongly, or shorted its terminal to the frame during installation, and blew all the filaments. Replace the tube(s) and try the counter. Take care with the installation of the "B" (high voltage) batteries! 5. There is a remote possibility that someone has mis-adjusted the high voltage set control that some counters have. Symptoms of too low a setting include no clicks from the headphone, no meter ‘kicks’. If set too high, the GM tube will ‘spill-over’ and you’ll hear a rough loud scratchy hiss and the meter needle quickly deflects to, and stays at maximum. If that occurs, turn the control down right away. Spill-over will ruin the 1B85, as spill-over ‘uses up’ the [organic] quench gas very quickly. The replacement 1B85 uses the CK1026, a halogen-quench tube, which will withstand spill-over, but it is never good to allow spill-over to occur for any length of time. The easiest way to set the high voltage without a meter is to reduce it as far as the control allows (probably counter-clockwise), then advance slowly until clicks are heard (cosmic rays). Note the position of the control, then advance it until spill-over occurs. Quickly turn the control down to stop spill-over, then set it to mid-way between the ‘just-starts-to-work’ and the spill-over positions. By the way, only a very special meter can be used to set the high voltage; it must present a load of at least 100 megohms to the Geiger counter high voltage power supply. Common VTVM, FET, and digital meters are only 10 megohms, and load the circuit excessively. See Hints section if you want to measure the high voltage. 6. If the counter seems to work fine, except the meter swings rather wildly (it’s supposed to move like taffy), then look for a cylindrical component about ½ to ¾ inch diameter, 1-1/2 to 2 inches long, a wire out each end. It is often located on the back of the meter. It usually has a thin cardboard wrapper, rolled at each end, and there is a "+" (plus) mark on or near one end. It is an "electrolytic capacitor", and is used to ‘dampen’ (slow down) the meter motion. Age causes it to fail. The value is usually 100 MF to 300 MF, at 3 VDC to 6 VDC. The exact value is not critical; for instance, you can use a 250 MF one to replace a 200 or 300 MF and the voltage rating can be 3 to 50 volts HINT: Electrolytic capacitors ("Electrolytics") are always suspect in older equipment.. if you spot another one in your counter, now is a very good time to replace it, as it is either bad now or will be shortly. Electrolytics are "polarized"; that means you must be careful to put the new one’s positive end to the same terminal that the old one’s positive end came from. Note that the new electrolytic may have its negative end marked ("negative", of course!), instead of having its positive end marked. Most U.S.A.-made electrolytics are marked "+" on the positive end, and for reasons only they know, almost all Japanese electrolytics are marked "- - - -" in a stripe on the body, pointing to the negative end. 7. Other problems include bad transistors (Victoreen Model 6, and 6A are famous for this), leaky probe cable (see if the inside insulation is sticky or mushy. You can often replace it with shielded audio cable, or with high-quality coiled cord. Radio Shack has several adequate audio cables and a coiled ‘microphone’ cable (278-356) that will work. HINTS 1. Always clean the battery terminals first, if at all corroded. It saves a lot of time and aggravation later. 2. Be very careful with any Geiger tube. Almost all of them have very thin walls or windows and that means that it is very easy to break it. Your replacement 1B85’s CK1026 is a thinwall glass tube, rather easy to break. Your Warranty does not cover breakage. 3. To make a simple test to see if the counting circuitry is working, use a small plastic-handle screwdriver. Hold it by the handle, touch the blade to the outside of the GM tube, then touch it to the center connection. Watch the meter, and/or listen for a click each time you go back and forth. This gives a fair test of the count circuit, and confirms there is some high voltage (it may not be enough for the Geiger tube, however). 4. If you really want to test the high voltage with a meter, here’s how: You will need a digital multimeter, (DMM) with an input resistance of 10 meg [ohms], four 20 meg resistors and one 10 meg resistor, and a 9 volt battery. Connect all the resistors in series, and place the ‘string’ of resistors in series with the positive lead of the DMM. Test that it is reasonably accurate by measuring a 9 volt battery directly with the meter, then measure it through the string of resistors. The readings should match numerically; only the decimal point will ‘be in the wrong place’, as the resistors, along with the input resistance of the meter form a 10:1 voltage divider. So if the 9 volt battery reads 9.41 direct, it will read .941 if the ratio is exactly 10:1. Now, if you apply the meter, with string of resistors in series to the counter, the voltage you read will be one-tenth of the real voltage: "91.2" is 912 volts. The reason you have to do all this is that the power supply in the counter will be severely loaded down by the DMM if it is used directly, (10 megs) but the 10:1 divider presents a 100 meg load, which most counters can support, thus the reading is much more accurate. 5. It’s nice to have a ‘sample’ that is radioactive to test your counter. Find a radium watch or clock in an antique shop or yard sale; it is not important that it glows (a lot of them don’t because the radium has destroyed the zinc sulfide that is the compound that makes it glow. But the radium itself is still quite active, and will remain so long into the future. A word of caution: all radioactive materials can be dangerous if not handled properly. A few safety precautions: Don’t remove the radium from the watch and put it into your pocket for extended periods of time. Always use disposable rubber gloves to handle a radioactive material (radium, mineral, etc.), or at least wash your hands well after handling. The main thing you do not want to do is to ingest the material! DON'T LEAVE RADIOACTIVE MATERIALS WHERE CHILDREN CAN REACH THEM! Always take the container in which you keep your radioactive materials outdoors, then open it.. Don’t open it indoors! Reason? Radon gas and its particulate "daughters" (other radioactive elements formed as a result of the disintegration of the radium) can build up in the container, and if you are inside with no appreciable airflow, you might breathe in a rather concentrated amount of it. Avoid ingestion!! Remember this simple rule: the intensity of radiation goes down very quickly with distance. Technically, it reduces by the square of the distance, so if you double the distance from the source, you reduce the radiation to one quarter what it was. Distance is always your friend. You can learn a lot more about radioactive safety from sites on the Internet. 6. If you want to save some money, you can make your own "B" batteries quite easily out of 9 volt batteries. Typical counters use the Eveready #455 45 volt, and #467 67-1/2 volt battery, and some use a small 22-1/2 volt battery, #412. You can get them from Batteries Plus (listed below), but the 67-1/2 volt battery is about $30 you can make an equivalent battery for about $9 plus a little work. You’ll need some solid bare wire, #22 or so, a soldering iron and solder, some electrical tape, and a little time. First determine how you’ll pack the batteries together to fit the available space. Then tape them into that shape, making sure that you line up the positive terminal of one battery next to the negative terminal of the next, to make wiring easier. Hint: since these batteries sometimes ‘leak’ (electrically) to the case, it is best to run tape strips between batteries to keep them from touching, then tape them into the ‘block’. Now, solder wires from positive of one battery to the negative of the next, placing the required number in series, five for 45 volts, seven for 67-1/2. Connections to the counter’s battery clips may be soldered, but clips found at the local radio store, or scavenged from the old batteries, is a much better way. Always watch polarity double-check it! Now cover the tops of the batteries with tape or a thin sheet of stiff plastic, and slide the assembly into the counter. That’s all there is to it! 7. Although the 22-1/2 volt battery often used in these counters is relatively inexpensive, you can make your own from two "23A" 12 volt batteries (used for auto door-lock transmitters). Make a holder for them out of wood or plastic; it should be about ½ inch thick, and 1 x 1.8 inches. Carve, mill or drill out the inside to fit the 23A batteries, put a brass pan-head phillips screw in each end for the contact. Solder a 1-1/2 inch insulated wire from positive of one battery to the negative of the other, and solder a 2 inch piece of wire on each battery’s other [free] terminal. Stuff them into the holder you made, wind the wire under each screw, and tighten. Wrap a piece of tape around the holder to retain the batteries if necessary. Now you can simply plug it into the counter’s holder. ******************************************************************************* WARRANTY The replacement 1B85 tube has been tested prior to shipment, and was found to be in good working order. This Warranty covers defects in parts and labor for a period of 30 days from date of purchase. Returned tubes, found to be defective, will be replaced, or your money refunded, at our option. This Warranty does not cover physical damage such as, but not limited to, crumpled envelopes and squashed or broken tubes. If you use it for a nail, run over it with an 18-wheeler, or leave it in your pants when you wash them, not only will we be offended, but your Warranty will be void. No other Warranty is expressed or implied. ******************************************************************************** SOURCES Here’s a list of places you can get parts for your counter. Prices are representative, being taken from 1997-98 catalogs, and may vary a little from those shown. NOTE: "MF" (above) and "uF" used below is exactly the same; MF is old terminology, that’s all. www.surplustuff.com He has tubes, capacitors, resistors, etc. Just about anything you might need, at very reasonable prices. Check out his website, and if you don't see what you need, send an E-mail. TUBES: 1U4 $2.00 1U5 $2.00 1T4 $2.50 3A5 $3.00 Radio Shack 9 volt batteries (expensive!) 23A batteries (ditto!) resistors, capacitors (electrolytics, at least). Coiled-cord. Check your local stores. MCM (1-800-543-4330) 9 volt alkaline batteries 290-080 @ $1.29 each in 10 qty 23A batteries 290-280 @$0.89 each high voltage capacitors: .0047 @ 1000 VDC (31-1590) 5 for $1.04 (these are ceramic type) .01 @ 1000 VDC (31-1610) 5 for $1.04 Electrolytics: 100 uF @ 16 VDC (31-050) $ 0.71 220 uF @ 16 VDC (31-060) $ 0.71 470 uF @ 16 VDC (31-070) $ 0.79 Digital Multimeter 72-6343 @ $14.99 (no kidding!) Mouser (1-800-346-6873 High voltage capacitors: .0047 @ 1000 VDC (5989-1KV.0047) $0.88 (these are wrap-and-fill) .01 @ 1000 VDC (5989-1KV.01) $0.93 Electrolytics: 100 uF @ 10 VDC (539-SKA10V100) $0.28 220 uf @ 16 VDC (539-SKA16V220) $0.29 470 uF @ 10 VDC (539-SKA10V470) $0.36 Batteries Plus (1-800-677-8278). See http://www.batteriesplus.com/ And use the locator for a store near you. * Snap-ring tools are available at any automotive parts store, and at many hardware stores. Hope this helps you get your counter working!