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Reg last won the day on August 22 2015

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  1. I've used a 7" widescan on most of the Tesoro's. I like it for really bad ground. In fact, I just gave a Sidewinder to a friend not too long after putting a 7" widescan coil on it. I need to see if I have another that you could try. Reg
  2. Hi fred, I know you well enough to know you are always a gentleman who always shows respect for fellow hunters. So, don't be bashful, I don't get upset any more. On a different note, since I have maybe 40 different detectors (most of them older models) I need to take Ron under wing and let him try a few of the newer ones I still have left to see what he likes. Unfortunately, I have been selling off some, so I don't have some of the more expensive ones any more. As an example, I recently traded my F75 Camo LTD for another TDI. I still have a few left like the MXT for him to try or maybe a newer Fisher Gold Bug. They are used for coin hunting also. BTW, I find the Fisher GB is fantastic in trashy areas. I have a couple of the SE models with the software just before they made the PRO. So, they are supposed to be basically the same depth wise. On the other hand, I don't think much of the Fisher F2. It doesn't work that well in this bad ground. Reg
  3. Once you feel you have the area detected thoroughly, I need to have you go over it again with a PI. I will be happy to supply the PI for you to try. Just to let you know, I pulled out a couple of merc dimes from that area late last year. On the upside, I didn't hunt the entire area. Reg
  4. A gold machine isn't necessarily the best option. For example, my brother tried using his GB 2 and that didn't work that well. Now, he is trying a newer GB which is a lower frequency and it works ok. The MXT might work a little better, though. As for your Tesoro line, I have used a lot of the older models and only one of the newer ones. They work fine but work better with a few mods. Like most detectors today, they added circuitry to compensate for what I call operator stupidity and that compensation does have its down side. Early VLF motion detectors had a direct relationship between the ground balance and the discrimination mode. The problem with everything being direct with no offset is in places where there are magnetite hotrocks, one could get a strange moaning signal when in the disc mode. People often thought there was something wrong with their detectors and sent them back to the factory to be "fixed". The real fix was to educate the operator and require him to make adjustments to compensate for the hotrock problem. Well, it didn't take manufacturers long to realize getting the people to understand wasn't going to happen so the simple solution was to adjust the detector internally to make this compensation built in. As such, an offset was installed that would shift the disc GB portion a few degrees so that when ground balanced in the all metal mode, the GB was really offset enough in the disc mode that hotrocks no longer gave a negative signal. Other manufacturers simply went to an internal preset GB for the disc mode that did the same thing. Your detector has no operator adjustable ground balance control, so it is a preset type. A quick way to tell on your Tesoro is to switch to that all metal (AM) mode and bob the coil. The audio should increase as the coil is lowered if properly set to minimize problems with hotrocks. In most places there is no need for this offset, but the exceptions cause enough problems with manufacturers they simply set them all basically the same. One thing Tesoro owners often do is "super tune" their disc mode. To do this you simply switch to the disc mode and turn the threshold to max. Now, on a Bandido or another Tesoro with a ground balance, you turn the GB to where the threshold goes quiet in the AM mode. Flip to disc and bob the coil and continue to turn the GB counter clockwise (more negative) until you get a strange moan when the coil is lowered. Then back the GB cw until the groan is gone. There is a third mod that can be done but it requires cutting and hacking the pc board. This mod adds a respectable amount of depth by sort of cheating. By cheating I mean, on a typical discriminator, there are two signals one is the all metal and the other the actual disc signal. Both signals generally have to be present with a good signal to produce an audio output. In a typical disc setup, this disc signal is biased off all the time and requires a "good" response through the filters. I change this and bias this disc portion on slightly. Thus any signal in the disc metal channel produces a good response. Why do I do this? Simple, iron signals are way stronger than non ferrous signals, so any ferrous junk easily produces a relatively strong negative disc signal, thus shutting off this disc channel by easily overcoming the offset I added. So, in simple terms, iron junk is still easily rejected but deeper questionable good signals come through as good objects. This simple mod added between an inch and two inches to the depth in the disc mode. I don't recommend anyone trying this last mod without extensive experience with pc board mods. It is all too easy to mess up a good board and make it difficult to undo. BTW, as mentioned by Fred, you can see I can't leave well enough alone. Reg
  5. Hi Fred and Ron, Well, since my ears were burning I thought I might jump in here and correct a couple of things. Ron, the guy I was hunting with (Jim) was using a factory TDI SL and i was using one of the SL type Super Pulse units that basically is a SL with two controls gone. Those two controls are the delay and the conductivity switch. This unit was originally built to be sold in Africa but the people over there are lacking knowledge of detectors so they try to purchase exactly the same as what is being used by someone they know. Ron, I have been out to the same park several times and haven't seen you out. Now, I spend a lot of time trying to get my brother (another Ron) up to speed on detectors. All the years my dad and I would go to AZ nugget hunting, my brother had no interest. Now, that our dad is gone and my brother is getting about as bad as me health wise, he decides to take up gold hunting. He went down to AZ last winter and found a few pickers with a new GB2 so now he is hooked. I had to laugh, the other day my brother was at the park trying out his new White's TRX pinpointer and making the same mistakes while expecting different results. For those of you not knowing, the TRX is a VLF based upon the MXT design. It has the ability to ground balance this device which is quite unique for a pinpointer. I find it has exceptional depth, which is one feature I really like. Oh yeah, it is quite sensitive to really small gold. Fred, how in the heck are you doing? Hope all is going well. BTW, Fred you are right, I talk too much but can't help it. I enjoy modding detectors and talking about what I have done to them. Now, I am having a difficult time leaving the Supe Pulse alone. I am getting used to hearing all tones and not being able to shut one off. Somene asked how bad is the ground here. Well, for a VLF it s really bad. Years ago George Payne designed his Mark 1 such that he could evaluate the mineralization of the soil using a simple technique. He had meter reading values for low, medium, high and extremely mineralized ground. Our ground at this park was easily extremely mineralized. This park sits above the Arkansas river and at the upper end of the Arkansas is ground extremely mineralized with magnetite. So, over eons of time, a lot of that black sand was transported down the valley. Years ago, I checked different areas up to 90 miles away down stream and found that within a mile or two of this river, the black sand type mineralization was extremely high. In such areas, a detector will not get super depth since the disc feature will begin to fail on coins deeper than 6+ inches. Those deeper coins will begin to read like iron junk. The dryer the ground, the worse it gets. Back in my VLf nugget hunting days, I figured out how to sort of make the detector cheat and gained a couple of inches in depth. It also made my old Lobo disc feature much more accurate on gold such that it would seldom error on it. I left that old Lobo with Tony Pancake for years and he found hundreds of small nuggets with it. I got it back from him some time back, but he missed it so much i sold it to him at a quite reasonable price. Reg
  6. JasonG, Do you repair your ML coils or just toss them? I suspect some can be repaired. Reg
  7. First, there isn't that much difference between the three TDI's. All are built on the same platform but mainly differ in features. For example, the TDI and the Pro differ in the fact the Pro has slightly different filtering which allows for a little better response to really small gold. The TDI comes with a dual field coil while the Pro normally comes with a plain mono. Also, the Pro has an additional GB control that works as a vernier, making it a little easier to ground balance in really bad ground. The SL is also very similar but has a noise reduction feature that makes the threshold very smooth and easy to use. Also, the SL uses a lower voltage battery system which includes using NiMh and AA Alkaline batteries. The dual field coil design gives the best of both worlds in the fact it gives decent depth while being more sensitive to small gold much like a smaller coil would do. Now, the fact is, it takes weeks to months to fully understand and learn the best settings for the TDI. Regardless of how well a person can run other detectors, the TDI is different and won't respond the same even though one might think it does. Next, the TDI isn't a ML and one of the things that simply doesn't work is trying to mimic the ML. Even using a larger coil requires different techniques and will have different results. The ML pushes the limits in the gain which results in the great depth it gets. The White's unit is more conservative and doesn't have the same sensitivity, thus doesn't get the same depth. On the other side of the coin, because of the lower gain the TDI can be used in noisy environments and is basically immune to many of the external signals that can wreak havoc on the ML. Also, the TDI was never meant to compete with the ML. It has its own unique features which make it unique in many ways. Simply stated, there are places and conditions where the TDI excels. In other areas, the ML clearly is the best unit to use. Personally, I wouldn't recommend older ML's as an alternative to the TDI especially for a casual or a weekend nugget hunter. The exceptions would be if a person doesn't care about possible costs of repair or doesn't mind buying a bunch of coils. Repairing the TDI is far cheaper and because of the design less likely to fail. I am in the process of selling a SD2200 simply because it isn't superior or even competitive in some ways to the TDI in my opinion and I have found gold with both models. Nvchris is correct, when using the TDI for coin hunting, depth will be lost if one wants to ignore most iron junk. However, using similar techniques for gold allows a person to lose very little depth on smaller gold while ignoring most thicker iron junk also. Most nails can be ignored while being able to detect gold up to 1/4 oz in some locations and well over a half oz in many other places. Testing once, twice or even a few times really doesn't let a person know what the TDI can do. It takes weeks to months to fully understand the best settings. So, the TDI is not for the person who isn't willing to put the time in or use the right techniques. A perfect example is most TDI owners sweep way to fast in areas where small gold is the common gold found. The Pro works a little better at faster speeds because of the filter difference. Fortunately, this is something that can be changed. Once again, the worst thing a person with a TDI can do is try to mimic what people do to their ML's. Reg
  8. You shouldn't have the detector automatically balance out gold with the GM4b. That usually happens with a detector that has an automatic ground balance system. However, if you ground balance over very small gold, it might happen. So, be careful on the ground balancing. Now, if the ground balance is not set correctly even by the slightest amount, you can easily miss very small gold in areas with a lot of black sand or even under some rocks having magnetite in them. You might experiment with this to see what I mean. Take some black sand and lay a small nugget in it and see if you can detect it. If you get even the slightest negative response from the black sand as you pass the coil over it, most likely you will miss the nugget. Get the ground balance right on the money or even with a very slight positive signal from the sand and they you should get a signal from the small gold you put in the sand. The ground balance thing is touchy when trying to hunt around black sand and does take time to master. Watch the videos for the GMT made by Jimmy Sierra. He points this black sand and gold problem out in one of them. Reg
  9. Ed in SoDak gave the best generic response. What he also said was very critical and that is, ideal sweep speed is detector dependent. Some VLF's work better when they are moved faster and the only way to know for sure is to some serious testing. The best approach is to use a very small target, preferably a non ferrous one. Next, bury the target. Yes, you can get an idea in an air test, but the in ground test also takes in other factors that are not easy to explain. PI's are different. Because an extra amount of filtering is used on a PI, the sweep speed is more critical for more reasons than one. Also, on PI's such as the newer ML's, the programs change factors than can influence that sweep speed, so again, the best technique is to do a little experimenting. The TDI is also very speed dependent and again, the ideal target is a very small piece of gold or other non ferrous object. Sweep too fast and small gold will be missed. The reason is actually reasons. One, the filtering is such that it has a peak at a certain speed. This varies a little between the TDI and the TDI pro because of a slight filter difference. The second has to do with the circuitry that eliminates half of the wee-woo response. Remember, on the TDI, the audio is either a wee or a woo. The corresponding second part of the wee-woo or the woo-wee is eliminated and filtering is involved. Sweep too fast and this filtering becomes an issue. Since most people use a Mono type coil on the TDI, the determination of the ideal sweep speed is quite constant. However, switching or using a DD coil does alter this ideal sweep speed. As for the "cone" theory on a mono, you might be surprised if you actually try to determine any front to back width between a mono and a DD. If you think about it, why would the transmit signal strength differ between the DD and the mono in terms of the theoretical field structure. Now, side to side or width of detection does change between a mono and a DD. This width difference also has a large effect on the ideal sweep speed. Experiment with it and you will see for yourself. One last note, too fast of a sweep speed has another serious problem on the ML. Swing over a shallow piece of iron trash and see how long the target signal lingers. While it is lingering, the ground covered is basically not detected for weaker signals since the stronger iron signal is still dominating. The two basic factors to determine the ideal sweep speed is to experiment and using common sense. Slow and fast are relative terms. A good example is fast to a nascar driver is not the same it is to the 75 year old neighbor driver. BTW, slow isn't the same for the two drivers mentioned. Both types of drivers require practice and experience if they are going to do the best they can. The same holds true for people using detectors. Reg
  10. Just for the record, the foldback design is something I designed a few years ago. It was my answer to the dual field design White's had that wouldn't step on the patent. Information of that design can be found on the Geotech1 forum, for those interested. I posted the basics as well as how to build one. The folded 8 as I called it allowed for one to have two different size coils in the same housing by using a figure 8 design where the top half of the 8 was folded back into the bottom half. Making the 8 lopsided would provide two different size coils, thus, better sensitivity to small gold because the smaller part of the winding would enhance the signal. The instructions on how to build coils as well as the original foldback design and even the materials used to build the first coil made by this guy were supplied by me. Fortunately, I still have some of the emails from that era providing proof for those who might believe otherwise. In fact, his first attempt didn't work because the wire I sent him was something I had not tried but recently purchased. It was Teflon coated wire that contained a strand of steel wire, something I didn't know even existed. Once I figured out what might be wrong, I sent him a different roll of wire, that did work. Here is a link to that post on the Geotech1 forum. http://www.geotech1....dual field coil Just drop down and read my posts pertaining to the figure 8 fold back design. I even have a pic showing the steps to make one. This was posted back in 2009. Now, with that said, don't expect coils built for the ML to act just like those built for the TDI. The TDI is very forgiving and will work with a wide range of designs, while the ML will not do the same. ML requires a coil have very stringent parameters to work properly. In other words, in simple terms, if you can count, solder and have a little common sense, you can build a coil that will work on the TDI. That is the beauty of this detector. Now, with that said, the reason I posted this is to just let people know building a coil for the TDI is easy while it is much more difficult to build properly working one for the ML. Reg
  11. Hi Tom, I use the TDI as well as the SL and like them both. No, they are not ML's but that isn't a bad thing. No, the TDI series will not go as deep as many ML's which is the big thing always mentioned. What the TDI has going for it is its ability to handle noise, hotrocks, black sand and be able to actually ignore a lot of the iron junk while detecting the size of nuggets most often found. This makes cherry picking targets quite easy in the worst kind of environments. In my opinion, most TDI's sold by owners are done so by people who have actually not used the PI long enough to fully understand or appreciate it. The longer one owns this detector and uses it often will find why so many people who have taken time to learn them actually prefer to use them. They work well and with experience will allow a person to hunt even trashy areas quite effectively. Better yet, they really do work well when trying to hunt old sites for silver and copper coins. To work best, the TDI needs to be operated slowly when compared to what a person usually runs a VLF. Sweep too fast and one can miss very small gold quite easily. Also, there is no need to operate or try to operate at maximum sensitivity. Learning how to adjust the GB to reduce noise and/or set the level of iron junk rejected is one important characteristic of this detector. Master this feature and you have come a long way in mastering the detector. Reg
  12. Complaining about not people in Michigan not being able to find more than .55 oz? WOW, keep in mind this what they can find on state land with only a permit. Try that type of prospecting or any other for that matter in your state on state land and see what happens if you are caught. Personally, I feel Michigan has some progressive recreational prospecting laws on state ground compared to many out here in the west. Most states including CO and AZ have laws stopping people from "trespassing" let alone recreational prospecting on state ground. Maybe we should ask our states to be more civilized towards the recreational prospector like Michigan. Reg
  13. I am going to offer a generic answer rather than offer a particular brand or model as the ideal ones to buy. Koss UR-30's work well but knowing why and more about the brand helps. So, first of all, Koss is a great brand for nugget hunting, but knowing more about Koss headphones in general helps because not all models even of Koss work that great. The Koss UR-30's are 100 ohm impedance headphones. The Koss UR-29's are cheaper are also 100 ohm headphones with a volume control. On the down side, the the UR-29's do not come with a coiled cord and the coiled cord is generally preferred, especially when hunting in brushy country. One of the big factors on which headphone's should be based is the person's hearing. Many older people have very poor hearing while a lot of other including some older people have quite sensitive ears. So, the ultimate selection can vary from person to person. For some, one model may not be loud enough while for others, a more popular type might be too loud. As a general rule the higher the impedance the louder a set of headphones might be. The impedance of a set of headphones has to do with the windings and wire size in the speakers themselves. Higher impedance usually means higher resistance if one simply measures the headphones with a VOM type meter. Unfortunately, there are exceptions to this higher impedance rule, so one does have to be careful. For some people the Koss 60 ohm units might work well, but, for others they may not be quite loud enough. What is worse is different brands having the same impedance may not sound or work the same. So, when in doubt, it helps to try them first to make sure they will work for you. Still, yet, people with great hearing can most likely use headphones in the 32 ohm range, which are one of the more common ones made today for detectors. Some of the more expensive headphones are custom made using Shooting protection style ear muffs normally used for hearing protection and installing the speakers and wiring. On these units, again a higher impedance speaker is generally used. Personally, I feel one should have some form of volume control on headphones since a person might use those same headphones on different detectors. On the plus side if you find a set of headphones that seem to work for you but they don't have a volume control, external controls are available and are not that expensive. Koss makes one that often sells for about $10 but usually a person will need adapters to go from the standard 3.5mm size stereo connector to the more standard 1/4 inch size found on most detectors. Now, the detector design does make a difference so some detectors work better than others when it comes to the lower impedance headphones. Even as the same detector brand evolves, quite often what works well may change, so there is no set rule. If you are a do-it yourself type of guy/gal, you can do what I do and buy cheap headphones with volume controls and a coiled cord and then change the speakers if the headphones are not lound enough. I may buy a used set of koss UR-29's cheap of Ebay and simply remove the speakers and install them in one of the cheaper set of headphones or I might simply change the cord on the UR-29's to a coiled type. BTW, quite often the volume control on the Koss UR-29's becomes erratic. Fortunately, an occassional spraying with WD 40 helps minimize that problem. One of the reasons I like some types of the cheaper type of headphones because they they are quite often made to withstand greater abuse. As an example, I have broken a couple pair of all plastic Koss units, but I still have some of my very old cheaper units that still work fine after over 40 years of use. For a person like me who has a detector for every occassion, then having a lot of headphones makes sense, especially because I prefer to have a protection bag for all my better detectors. To assure that all I have to do is grab a bag and go, I try to have extra batteries and headphones in the bag with each detector. Just to let you know what I am talking about, here is a list of the different detectors I own and quite often use. The TDI, and the TDI SL, the MXT, the GM 4, the GMT, are Whites models. Then I have the Tesoro LST and a modified orignal Lobo that really kicks butt. Of course, I have Fisher's also and that list includes the GB 2 and the new GB SE as well as a F75 LTD camo version. Yes, I have a couple of ML's including the XT-18000 and a SD-2200. I also have a couple of home made low power PI's that have some really unique features. Along with the just mentioned list I have a few dozen other detectors primarily made for coin or relic hunting. Last, I have some older Eric Foster PI units that can work for gold such as a couple of GS 5's, two GS 4's and a modified Beachscan PI I built up for my late signficant other who wanted something super light. That little detector weighed less than 3lbs total including coil, battery and control box. So, as you can tell, I have enough detectors to let me know not all are the same or recommend when trying to decide what headphones to use. Reg
  14. Hi Bill, PI's have basically one way to ground balance and that is to take different samples and subtract one or more from the main sample such that the subtraction signal equals the main signal for the object you want to ignore. Normally, this adjustment is done to ignore the ground signal. So, in the case of the TDI and the SD's, a later sample was taken, amplified and then that signal was subtracted from the main sample to eliminate the ground signal. When this technique is used, some objects will create a high-low signal while other objects will cause a low-high response. Just which signal occurs has to do with the relationship of the object and the ground signal decay response. On the TDI, if the object that is being detected has a longer decay time than the ground adjustment position than the response will be a low tone. Smaller objects or materials that have a short decay time will create a high tone. Now, usually the ground adjustment is set to ignore the ground, so when that is the case then any object having a longer decay time than the ground will create a low tone and objects that have signals that decay quickly like small gold will have a high tone. On the ML's, expecially the old SD 2100 or earlier, this was also the case. Later ML's probably used a very similar technique but altered another parameter or two such as just how long after the main sample is taken they take the second sample used in the ground balance circuitry. Change the time delay between the two samples and you will change the relationship of the ground signal and the target signal. What this amounts to is at one setting, maybe a target will give a low-high response, but on a different timing setup, that same target will give a high-low response. ML owners might want to do some testing to see just what happens when different settings are used and should do this with a wide range of targets just to see if some of those targets change tones as the detector is adjusted. One can think of this ground balance thing or target tone change thing as simply two signals that are the result of two different samples and those samples are amplified at different amounts and subsequently one signal subtracted from the other. So, if we have signal A and signal B with signal B subtracted from A, and signal A gives a high tone and B gives a low tone, then if A is bigger than B, the summation will be a high tone or on the ML, a high-low response. If signal B is greater, then the subtraction process will create a low tone on the TDI but maybe a low-high on the ML. Now, keep in mind that ML may have an inverted signal already as well as the ability to invert signals, so in some cases, what is a High tone on the TDI, maybe a Low-high tone on the ML. Personally, I have not had one of the later models of ML's in my hands long enough to really know for sure just which way it is. Now, with the above info, we know if two signals are subtracted from each other. the tone will be either a low-high or a high -low response. The exception will be when the two signals are exactly equal and at that setting, just like what happens to the ground signal, one can have a good target not generate any or much of a response. Now, getting back to the question as to why a meteorite might not have a common tone, well that is simple, the meteorite is clearly different in its characteristics as far as the detector is concerned. Since something as simple as a stony meteorite can vary dramatically which is noted in the L or H numbers, meaning the amount of nickel can be scarce or it could have a large amount of this metal. The results would be one would clearly have a much stronger signal than the other. The more nickel the stronger the response, the longer the decay. If the concenteration of nickel is sufficient, then it could easily change tones. So, the chemistry and characteristics of the meteorite as well as the size clearly will play an important part in how the space rock sounds off. Now, for those of you who have a ML and also have a wide range of gold nuggets, you might test to see which common size creates a high-low tone and which creates a low-high tone. Then if you have a bunch of different timings or settings on the detector test each nugget with all of the settings. I suspect you will find certain nuggets just might change tones as the detector is adjusted. Believe it or not, knowing this and just what is going on when the detector's controls are adjusted is very important if you want to get the greatest depth out of your detector. What complicates matters is the fact that nuggets vary dramatically, so you may have two almost identical size nuggets that act totally different and this be normal. The variable is the nugget itself. So, in very simple terms, the detector is telling you something about the target with the tone you hear. Just what it is telling you can only be known by knowing your detector thoroughly as well as the gold characteristics. On the TDI, I found I could easily tell Rich Hill gold from that found over at Model Creek just by the sound even if I wasn't able to see the gold but knew the approximate size of the nugget. In other words, two identical weight and size nuggets with one from Rich Hill and the other from Model Creek would respond totally different. Again, this is completely normal. Reg
  15. Hi Frank, I had forgotten about the post that was on another forum pertaining to coil current and battery life, but even though that post is a few years old, the fundamentals still stand. ML detectors are very finicky about what coil will work on them, so as a general rule, the inductance and resistance remain the same regardless of coil size. As mentioned in the other post, there can be some variation between the DD's and the Mono type coils but this can occur because on a DD, the receive winding is the winding that plays an important part as to whether the coil will work or not. In the case of a DD, one can vary the inductance a little more and still get the detector to work ok. This was pointed out by Robby H. on the post on the other forum. However, even as he stated, the change is very little. One other interesting post on that other forum indicated the ML average current draw to be about 0.8 amps with variations of up to about 0.1amp. So, in very simple terms, the current draw is over 3/4 amp and usually less than 1 amp per hour. Now, with all that gobbly-gook out of the way, the basic rules still apply and that means because coils have basically the same resistance and inductance regardless of their shape and size, the results will be the same current useage. We have a tendency to try to think in common sense terms and not so much in technical terms, especially if the technical training is not there. This is what makes us human and always trying to find an answer to a problem needing technical training to better understand. As a perfect example, if you run a battery down froma full charge does it weigh less? Think about it, something changed, right? Well, that is off the subject a little, but when you read all the different posts on this thread, there are some good answers relating to battery life to keep in mind. One good one has to do with external amplifiers. If that amplifier has its own battery then the detector battery useage is or should be minimal. As mentioned before, some typical battery currents of a ML PI were in the .80 amp range. Now, if a person uses a 7800 ma battery which is the same as saying it is a 7.8A battery, will the battery last almost 10 hours? The simple answer is no and that is based upon the fact that most batteries are rated based upon an ideal current draw. Change the amount of current used and the battery life can diminish quite dramatically. Actual battery life at heavy current drains can reduce to half time or so and in doing so, the internal battery resistance can become a problem resulting in detector stability. So, in simple terms, a 7800ma battery may only last 4 to 5 hours continual use and still be be in good or at least usual shape. Just so you know, the typical current output of a Li Ion 18650 cell is about 2600 ma or 2.6A at 3.6V. So, for a 7.2V battery we have two cells in series. Now,, if you want a 7800 ma battery rated at 7.2V, there will be three battery stacks in parallel (where a stack consists of two cells in series). thus, there will be 6 batteries that could fail. What makes things worse is the ease of buying lower priced batteries with claims of having the same battery life as a quality made battery. A cheap chinese knockoff, as a general rule will not last as long or work as well as a quality made battery from a different source. All of this is compounded by the fact that when a battery pack fails, it usually is because of one weak battery giving up. Since the batteries are usually in series, then one weak one renders the entire pack useless that is made up of only one series stack. In the case of multiple batteries in parallel, one dead battery drops the effectiveness signficantly, thus one will experience a shorter run time. Finally, if battery life is something one is trying to increase, then when you stop detecting, turn the machine off, even if it only for a few minutes at a time. You would be surprised at how much battery drain can happen if this simple rule isn't followed. JasonG pointed out something to keep in mind and that is, the edge of a large coil allows a person to detect small gold quite well. No, you won't get dramatic depth but a few inches is better than trying to detect that same nugget by using the center of the coil. Try it and you will see what I mean. Now, knowing the edge of the coil can be the detection zone for very small nuggets, can anyone now better understand how one can dig a deep hole before finding the nugget? The bottom line is the nugget isn't where we think it is. Now, for those of you who still want to check for themselves on this coil size and battery current, I strongly recommend you use non contact test equipment. In this case, a simple clamp on ammeter that uses an inductive pickup works quite well and is reasonably accurate. Here is a link to what I mean. http://www.ebay.com/...=item1e6641e475 There are lots of clamp on meters but most do not read DC current, so be careful when buying one if that is your purpose in buying one. Personally, I like the DC current clamp on because I can even read the battery current draw of a vehicle without taking a battery lead off. Just clamp the jaws around one of the leads coming from the battery and read the current. This is about the safest test one can do and should be accurate enough for what you are wanting to know regardless if you are checking a detector or your car. On the detector, use an old lead acid battery hookup for the easiest access to a battery lead and clamp around one of the battery leads and you should get an idea of the current drawn. Change coils and you should see little to no difference. Reg
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