Reg

Finding the amount of reduction of the conductivity of gold as it is alloyed has turned out to be quite difficult. Fortunately, I did find some shocking information on the old PI forum that does help. Here is that info. Eric Here are some numbers for copper-gold and silver-gold alloys. The first column is the % of gold in the alloy. The second column is the conductivity relative to copper of the copper-gold alloy. The third column is the conductivity relative to copper of the silver-gold alloy. % au cu ag 100 .75 .75 90 .14 .23 80 ??? .17 70 .11 .14 60 .12 .14 50 .14 .15 40 .17 .17 30 .22 .21 20 .30 ??? 10 .47 .44 0 1.0 1.05 Lead shot is usually alloyed with antimony, so its conductivity is less than pure lead. Robert (The above info was posted by the late Robert Hoolko). Hi Beachcomber, Alloying even a few percent of other metals causes the conductivity of gold to drop dramatically. Even if the other metal is a good conductor, like silver. I haven't seen any published values for the different alloys either. I have a conductivity meter which gives a reading as a percentage of that of annealed copper. A 9K ring gives a reading of 18%. Unfortunately the object has to have a surface area of about a square centimeter, otherwise you do not get enough signal to read. This is a very wide ring, so it can be done. No other rings I have work. Great for coins though, a nickel reads 5.3% Eric. As an example from the chart we see that gold can go from a reading of 77 at pure gold to 16 when alloyed with silver such that the gold is only 75%. The 16 reading would place that same gold closer to the conductivity of lead, while the pure reading is much closer to copper. This last post refers to a website where standardize gold alloys were listed by a company, deringerney, in 2010. Hope this info helps. Reg

The answer you are looking for is both simple and complex. I will try to explain the simple part. First, whether a target is a high or a low conductor is determined by the GB control and just where it is set. If the GB is set so the ground signal is nulled, then any detected object that generates a low tone has a longer time constant than the ground signal. This results in the GB signal channel being greater than the metal response channel. Thus, the summed signals results in a negative response, and this results in a low tone. In the case of gold nuggets this means the nugget has to be pure enough, the right size and density and often the right shape or right surface characteristics. Over the years, much of the gold I found came from Rich Hill AZ. Fortunately, this gold is quite pure (92% or so). As such, gold larger than a quarter OZ was large enough to generate a low tone. All gold smaller would create a high tone,. Early US gold coins follow this pattern, meaning a $5 US gold coin would or could fall in the GB hole and be almost not detected. All lower valued gold coins would be a high tone or a low conductor. As the purity of gold is reduced, the conductivity of the gold diminishes, thus, much if not most is detected as low conductors. A good example is the gold we found about 5 miles from Rich Hill where all the gold found registered as low conductors even up to the 1 oz nugget found. At this site almost a pound of gold was found with many of the nuggets greater than 1/4 oz and all tested with the TDI registered as low conductors. Reg

For those interested, the QED is real but was held up by a bunch of BS from ML. Untimately, Bugwiskers modified his GB technique and ML signed off on their patent complaint according to Bugwiskers. So, yes, the QED should be in production soon if not by now. On the down side, some of the soldering is done manually so production is slow. Maybe Whites will offer to help and make them here. It would simplify their need for a newer model of the TDI. Hey, maybe tboykin can help with that. He will need to keep John Earle out of the loop, though. To answer a question asked by Steve H about whether the QED has the high low tone like the TDI, I highly doubt it. Bugwhiskers used a multiple sampling for the GB to reduce any depth loss and minimize any hole. At least, that is my guess. Reg

Who told you the parts are obsolete? What parts? I would like to know? Reg

tboykin, Your questions and suggestions can be answered easily to improve the SL. First, contact RNB and have them build the SL Li Ion batteries but use the Panasonic 3400mah batteries. Option 2 would be to add an under housing mod to hold external battery and a connector so an external 4 cell battery could be used. As for not working in hot ground, simply modify units with my mod needed and installed on SPP OZ units. Whites has the details already. This makes the SL GB as smooth as the TDI. Older units already made and in use can be upgraded easily for a reasonable cost for any unit out of warranty. Modify the filters to allow for a faster swing speed (Reduce value of C20 and C21 from 0.47uf to 0.22uf). This makes the SL a poor man's mini Pro model. Right now, the SL is crippled because of the filtering and trying to sweep to fast causes serious depth and small gold loss. Have Miner John build a couple of different sizes of the folded mono design and minimize selling the Whites dual field design which doesn't ground balance well in bad ground. Add a relic model and a separate gold model so relic hunters do not have to buy the dual field coils. Dual field or folded mono are stupid for relic hunters since they don't need to find tiny objects. FYI the folded mono design is something I came up with in July 2009 (http://www.geotech1.com/forums/showthread.php?15585-Coax-for-duel-field-coil&highlight=dual+field). Just look for the jpeg of the different dual field design. Change software to allow reducing the delay but either do so with a separate switch or mark the delay setting in RED where there may be a problem using the large coils. Add a switch to give and option to eliminate the third filter right after the GB summing junction. This will eliminate the loss of small gold signals because of this filter interaction. Do these mods and you will give the ML 2300 a real run for the money. Reg PS you may have to remove C69 located between U1A and B when you lower the delay for proper operation.

Hard Prospector, I use the TDI and SL but that won't stop me from pointing out their weaknesses or limitations. I prefer people know the truth and any solution available if there is a weakness. In fact, I want people like John to point out what they see as weaknesses. I just want that information to be as truthful as possible. It is when people like John point out things that cures or corrections will come to light making a better detector in the long run. Unfortunately, the present management at White's and I no longer have any communications and, in my opinion, there is no one at White's who knows much about the TDI series or how to make it better. Instead, I suspect they will scrap the present design if and when they come up with another rather than listen to dummies like me. Reg

John, You should be able to detect a Morgan dollar farther with the GB on than off. The reason is, the GB circuitry amplifies the signal well over 30 times more in the GB channel than what is happening in the main channel so when the GB is on, the summed signal is amplified more than when the GB is off.That is why the signal is a low tone. If the GB channel signal is stronger than the main channel signal, you will get a low tone. Sum the GB channel and the main channel and if the tone is low, the target will be detected deeper than if the GB is off. So, that is normal. As to your claim of 15" on the first three passes or so, there may be some truth to this but not for 2 or 3 passes as you mentioned. I just tried an experiment and if all is quiet and run an air test, I think I get a signal extending out to the 15" range but only on one pass. Any further passes are at the 12" range. Wait a second or two between passes and they can hit 15" again but not for more than one pass. I am guessing that changing and/or removing a few components plus shorting out a couple will minimize this situation, which is something I recommended some time back as part of the Aussie fix. If you know a good technician with equipment to work on surface mount parts, then I can offer some suggestions. I absolutely do not recommend a person work on the SL without extensive surface mount experience. Try your test again and see if it dies at one pass. I also think your detector is probably working ok and is not possessed. Reg

Why do you sweep faster with the TDI Pro than you do with the ATX? If you do this with the SL, it will not work the same as the Pro and I explained why. Again, there is no smoothing feature caused by any special circuitry outside of simple capacitors that are there regardless of whether the GB is on or off that will cause any smoothing when the GB is turned off. So, I have no idea of what you are experiencing or why, but I can tell you with absolutely certainty, there is no special smoothing circuitry activated when the GB is turned off. That is what I am saying and watching a video of the ATX won't change that, especially when talking about the SL. Feel free to make a video yourself of the SL and show what you say it is doing wrong. That might help. You can't sweep the SL as fast as you do with the Pro and expect it to function the same. As I said, the SL filtering is slower and will not have the same results. This difference in filtering is well known and was mentioned as one of the differences between the TDI and the Pro. The TDI will not work the same as the Pro either, since it has a slower filter speed like the SL. Reg

I really hope people do not believe the TDI or SL has all the features mentioned because they don't. First, the main difference between the TDI and SL is the noise reduction circuitry that reduces the warble, and the fact, the two have different voltage supplies. There is also a filter speed difference between the Pro and the SL, but not with the regular TDI and SL. Now, the Pro does have a different filter speed than the SL and that causes some of the problems that should be eliminated. There is no smoothing circuitry outside of the usual capacitors in this design once the GB is turned off. In fact, there is no smoothing circuitry since the warble and typical noise and warble happens because of the extra gain in the GB channel and when the GB is turned off, the GB channel is basically dead and typical warble and noise will not exist. A couple of years ago, a simplified version of the SL was introduced to Australia and soon after its introduction it was determined this detector had what was commonly called a "hiccup" that was aggravating enough, many people were wanting to return the detector. I was asked by one of the people over there if I would help them find a solution, which I ultimately did. One of the recommended solutions was to eliminate an extra filter found in both the SL and TDI versions. Why eliminate this filter? Simple, the filter has a very slow time constant so this filter would or could interfere with the autotune filtering causing some very weak signals to be compromised at certain sweep speeds. In other words, the filters would buck each other at times and very weak signals suffered. Unfortunately, eliminating this additional filter caused an increase in gain that would result in increased noise and the preset threshold setting to not be properly set. This caused concern and the filter was left in thus causing its own problems. Does the SL have its own design weaknesses? Yes, but many that caused the "hiccup" problem in OZ are now removed on later units. Because the problems that caused the hiccup in OZ didn't cause problems here in the US or Europe, no recall was needed. Reg

There are different TDI's even though the gain of each is basically the same. First there was the through the hole TDI which is basically a GS 5 with a couple of mods. Then came the standard TDI which was followed by the TDI Pro and finally came the SL series. Each is a little different in filtering and/or sampling timing. The result of the minor changes could be seen in testing a series of targets of different size and material types and noting the differences. In most cases, one would see little or no difference, but in other cases there would be subtle changes. Now, the differences show up on coil responses also. For example, a ML compatible DD coil may work reasonably well on the GS 5 but not on the later TDI's well if at all. The problem lies in the fact how the different TDI's react to the heavy current of the ML coils and the delay of the detector. As for the delay, the early TDI's and the later surface mount do not have the same minimum delay. But, but but, all models say 10usec is the minimal delay. Well, it depends upon just how you interpret when and how the delay is measured. In other words, if you use the original TDI procedure, then the original has a 10 usec delay and the later units have a 13 usec delay. This small difference affects both small gold detection but also how well a ML DD coil works on that detector. Now, add filter differences and other subtle changes show up. Take the fact the TDI has both low pass filters and high pass filters and if they overlap, certain things can occur. The TDI Pro corrects some of those problems by altering a key low pass filter setup. This filter change helps in the detection of small gold but also helps in sweep speed detection. This helps in using larger coils providing a faster sweep speed is used. Take a large coil and place it on a bench and then take a small coin and pass it over the coil at different speeds. As you increase the speed, you will notice the signal get louder if the coin is held at or near maximum depth of detection until it reaches a point where the signal will begin to fade again. Do this test with a TDI and the Pro and you will see a noticeable difference. In simple terms, the assumption that a TDI doesn't have enough power to power a large coil is totally false. Instead, the interaction of the filtering inside the detector is the culprit. So, what does this mean? Simple, modify the filtering and you could use larger coils much easier. you may have to put up with more noise if you don't try to reduce the noise at its sources though. Now, when it comes to coils, the TDI is forgiving but works best with coils made for the TDI and not ones made for the ML's. As an example, ML DD coils don't work well on the later TDI's or earlier TDI's if the delay is turned up a little. However, DD coils made to work on the TDI should work fine. In fact, some are being tested and used in OZ right now. One final note, the SL has extra pads where extra parts can be added in certain filter locations. This would make modifying some filtering easier. Reg

Hi John, Sorry if i sounded like I was picking on you. I simply want people to know that just because someone says something isn't so, doesn't make it correct. Now, for those wondering, the SL and the SPP use the same mother board part for part. The difference is in the software where the delay is fixed on the SPP and adjustable on the SL. The other difference is there is no conductivity switch. Since the conductivity switch is is totally part dependent, then adding a switch with the proper connector is a simple doable procedure. As for why you never saw a video of the SL with a hiccup, the answer is simple. White's never knowingly sold the SL in OZ. The only TDI series detector authorized to be sold in OZ was the TDI Pro. Then, Jimmy Sierra purchased a bunch of the SPP's (with a different name) and renamed them the SPP. Shortly afterward, he began selling them in OZ via the distributor there. Once they began to sell in OZ, the "hiccup" began to show up. The owners tried many things including adding a 10 turn control to the GB, like the one shown on the video you posted. Regardless of what they tried, the problem still existed. Then a guy named Luke Lindsay contacted me and asked if I would help. Well, no matter what I did over here in the US, I couldn't duplicate the problem, which obviously, made fixing the problem impossible. So, I had Luke make several videos and send them to me and I began to troubleshoot the problem remotely. Fortunately, Luke had a good electronic background and sufficient test equipment. So, I came up with several ideas and, with Luke doing the work and testing in OZ, we were able to find a solution to the problem. I will say it again, Luke was a key reason the problem was resolved. Without his help, I wouldn't have been able to find a solution. I would also like to thank the former CEO of Whites, Alan Holcombe, who through his support to me by providing what I needed just before he retired. Unfortunately, that cooperation ceased once Alan retired and it took a while before White's incorporated the needed changes. Also, any and all communications between me and White's ceased. I quit trying to communicate with anyone there once I was told their technician refused to take my call before they finally tried my solution. I figured it was time for me to quit wasting my time with them. For anyone, especially a nugget hunter wanting to try a low priced PI, the SPP is a perfect choice, especially if one wants to buy new. Remember, Jimmy Sierra is the key supplier to OZ of Whit'es equipment and his willingness to buy the SPP is the key reason it was in OZ. Once Alan retired, I continued just to help Jimmy. To me, Jimmy Sierra is a legend and has spent most of his life promoting White's metal detectors. He is a legend that deserves respect. For those of you who don't know, Jummy is one of the key reasons for the existence of theTDI series of detectors as well as the MXT and GMT. The SPP also woks well for anyone wanting a PI for beach hunting. Turn off the GB and add inches to the depth. Since the SPP coil is a plain mono, it works better than the dual field in ignoring small junk. The SPP originally came with the 12" mono and a 6" mono. I am not sure what it comes with now. Reg

Sorry John, you are incorrect. There is no desensitizing of the machine. In fact, the primary signal is the gold channel which is what is used for the TDI when the GB is turned off has absolutely nothing done to it. The main culprit for noise is the GB channel because of the needed gain for ground balancing. The mod modifies the GB channel only. The source of the noise can be from external EMI or it can be from internal components with the preamp the main area where the noise is generated. So, if we neglect the external EMI, then the main noise comes from the preamp and associated components. Replace the preamp with one that has a dramatic reduction in noise output and part of that noise is eliminated. Then other changes simply bias the GB channel such that the noise is shut off or nearly shut off but not so much that the GB doesn't work right. Oh yeah, there are other ways to minimize the noise, but I will leave the design to you and others. My generosity with White's or others has been terminated. I understand you don't believe the "hiccup" problem with the SL or SPP exists on other units not sent to OZ. Well, if you ever get back to OZ, you will find out differently, especially if you don't get your unit modified. Reg

Jasong, The "iron dust" toroid ferrite that meets the general specs (mentioned in their white pages) of the ML ferrite used on the ZVT is a simple powder iron type and most likely is a -6 type. The color usually gives the type away and the one used by ML is yellow. A T106-6 is a 1" toroid. A T80-6 is one that is .80" od. So, if you know the approximate diameter of the one used by ML then if the OD is 1.5" then a T150-6 most likely would work. Like mentioned before, most likely, the ferrite won't be needed here in the US in most places. Our soil conditions are generally nothing like those in Oz. However, since anything is possible, there may be an isolated place or two where a ferrite might help. Reg

Hi Sunriseboy, Yes, there is a guy in OZ that does mods. His name is Luke Lindsay. He can add a mod that reduces the warble making the detector much quieter. To know more about what his mods do, you can look at his you tube videos he lists under lukeozdigger. Unfortunately, he is in the process of moving right now, so catching him at a time when he can do the mods may take a while. Luke posts on many PI forums including a couple in OZ. Usually you can catch him on the TDI and goldmaster forum. Just google the forum and you should get a link. Reg

Why not ask Minelab to provide the specs of the ferrite ring so people wanting one can purchase their own from a third party? Providing something as simple as it is a soft ferrite material and the typical number of that ferrite or it is a powdered iron material would help those wanting to get their own. Reg

Some people might think what is happening is not explainable but there really is a simple explanation. What is interesting is the reason these same coins were not found with the best of VLF's is the same basic reason and that is masking of a target by another target. Unfortunately, trying to explain it could easily take a book or at least a chapter of information. Now, with that said, my response will be shortened considerably from what is really needed, but I will try to supply the gist of what happens and why. Turn the delay to 10 usec and use the All mode and you will hear both high tones and low tones over the ground Mark is hunting. I know, Mark sent me a sample of the "dirt" for me to test. So, why did advancing the delay suddenly cause the low tone "good" targets to be heard? Again, the answer is simple, the high tone signals diminished sufficiently such that they were no longer a problem once the delay was advanced. When you ground balance the detector, you end up with the ground signal balanced out. All targets that are high tones have a target characteristic shorter than the ground signal. By target characteristic I mean if the intensity of the target is the same as that of the ground, then the signal would decay faster and would disappear before the ground signal because of the delay settings. Increasing the intensity of the target signal causes the balance point to also be increased Ever go over a camp fire place location and notice the ground signal increases? Now, some of you may think you are detecting the old pieces of burnt wood, but that is not the case. You are detecting the ground minerals that have transitioned because of the heat from the fire. Because the intensity of the ground signal has increased, then a simple small advance of the ground balance control will cause this increased ground intensity signal to be balanced out. Normally, a weak gold signal will not balance out this way. Getting back to the ground where Mark is hunting, changing the delay and not the ground balance has a similar effect. Advancing the delay can cause weak high tone target responses to diminish. If such high tone targets diminish sufficiently, then deeper good low tone targets will become he dominate signal and will be heard. If the high tone signals are small weak targets then even raising the coil rather than scraping the ground can cause such high tone signals to diminish sufficiently that they are no longer a problem then either. Since coin size objects will normally be detected deeper by using a larger coil, then the use of a larger coil plus raising the coil some may not require advancing the delay. Fortunately, copper and silver coins have a very long time constant, that advancing the delay cause very little depth loss. So, often it is advisable to advance the delay also. So, a simple response to Mark's problem would be to advance the delay sufficiently. Then use a larger coil to reduce small signal responses, and finally, raise the coil a little. So, how much should you advance the delay? Well, that takes practice but a simple turn of the delay control and listening to the high tone signals will help. Advance the delay sufficiently that the weak high tone responses diminish if possible or at least are reduced noticeably. In summary I have mentioned advancing the GB when checking ground hot spots, advancing the delay when eliminating weak high tone signals, using a larger coil to reduce weak high tone signals, and finally raising the coil a little. In Mark's case, advancing the GB is probably not advisable. Instead, selecting High conductor and reducing the GB while increasing the delay will most likely be the best solutions. Add using a larger coil plus raising the coil while hunting just may help also. Steve is absolutely correct, experiment, try different settings of the controls, but more importantly, learn just what each coil does or is supposed to do. The controls are on the detector to be used. The key is to know when and why a control should be moved. Reg

Hi Jim, Did you ever find a battery adapter for your XT18000? If not, let me know. I finally cut some pc board but still have to make the adapter. Now, if I remember correctly, there really isn't much difference between the MD10 and the MD20. So, any instructions you can find on their should work on the other. There is a video out showing how to use the MD detectors and basically if set up right, you power to probe and if you get a good signal, it is probably gold or maybe lead. If you pull away from the target and it sounds off, it is most likely a piece of magnetite. The next thing is to practice some to get the feel of the detector but it is quite simple. Reg

Hi Patrick, How in the heck are you doing? Hope all is well with you. Reg

Hi Tom, I talked to my buddy and he is not familiar with the Tesoro schematic or pinout so he really doesn't want to tackle your project. You might try to find someone who has an Eric Foster ferrite probe he built for the GS 5 and then try to find a used coiltek switchbox and use that combination if you still have a TDI or SL detector. I know that probe has decent depth. Tuypically, you can detect 4" to 5" on a dime size object but it will detect small nuggets too. Reg

Steve, Thanks for posting the info about the bigfoot by Jimmy Sierra. I had forgotten about it. Reg

Yep, I am in Pueblo. Reg

vanursepaul, There are things that can be done to the SL to improve it and I am pretty sure Digger Bob has them done to his units. The reason I say this is because I modified a SPP and that unit was sent to Digger Bob for him to evaluate. Bob has some of the worse ground in his back yard that approaches that found in OZ. What he found was the modified SPP ran smoother and was easier to ground balance. He probably knows if all newer SL's are modified or not. Now, there is a guy making 4 Li Ion cell batteries for the SL that increase the gain so it is much closer to the TDI. My buddy can make mods to the SL also and one of those mods is to change the filters so it is more like the Pro. This makes the detector a little more responsive to small gold. Reg

Vanursepaul, The SL has noise reduction circuitry to reduce the noise but it has its own quirks. Fortunately, they do not cause much of a problem here in the US. However, any SL going to OZ should be modified to eliminate the "hiccup" that happens over there because of the SL noise reduction design. It is my understanding that SL's made after November of last year have this hiccup mod, but I can't say that for sure. I have no communication link with White's any more. Reg

Ivanwho, I don't do the mods myself. My hands don't work that well any more so I have a friend do them. He does the work and keeps all the money since the mod is somewhat labor intensive and does require a pcb trace mod. A full TDI mod costs about $125 (return shipping included with $500 insurance) and that includes replacing the preamp with a much better IC, the addition of a small pc board to reduce the noise, a filter change so the regular TDI is upgraded to the filtering of the Pro for a faster response. The mod also includes calibration of certain stages to 1 millivolt to assure the mod works as designed. This TDI pro filter mod makes the regular TDI like the Pro but without the extra GB pot and volume control. The volume control was added to help reduce the noise problem, but with the noise reduction mod, is not needed for that purpose any more. One additional mod is to short out a capacitor which eliminates a third filter that is not needed and can cause weak signal problems. This mod does increase the gain which in turn increases the noise level. Fortunately, reducing the gain using the gain control about 20% or so makes it back to normal. You do gain a little depth but more noise with this mod. One advantage of this mod is weak signals become more reliable. Reg

Hi Rick, Glad you like the mods. They really do help for those who have never heard of them. Besides more depth because of the reduced noise, they set the base for a new DOD coil that will really help the TDI. Right now, the coil is in the development stage. My prototype shows you won't need any GB in many places so you can turn the GB off and gain that extra depth. The down side of the coil is the signal strength is not that loud so a good set of headphones is required for maximum depth. The big advantage is the super quiet threshold. It is so quiet, I am thinking of cranking up the gain to add even more depth. Now, as for your wanting a dead Bigfoot coil for the housing, you can buy 3 different sizes of rectangulart coil housings just up the road from where you live in AZ. Bill Hays makes three sizes of rectangular housings and he is in Prescott Valley. The three sizes are a 12" by 3 1/2", a 15" by 3 1/2" and an 18" by 5 1/2". He sells the larger one for $16.50 and less for the other two. Shipping is extra. His phone number is 1-928-772-2624 for those interested. He may not answer because he gets so many solicitor calls, so leave a message and he will get back to you. Building a mono bigfoot is easy. Just shield it right and it should work fine. If you want to get a little fancier, you can build a big foot ground and noise cancelling version. This one requires a rectangular mono tx and a figure 8 RX winding. This design should be extremely quiet and require little to no GB signal. Only half of the coil will create a signal on the TDI, though. So, there are new things in the works for the old tired TDI. Reg