Tesoro's New Lobo Metal Detector
By Reginald G. Sniff
From Page 8
July, 1990 issue of Lost Treasure

The new Lobo is the latest addition to the Tesoro line of metal detectors. Like their Diablo, Tesoro designed the Lobo as a gold-hunting detector. This new detector has other similarities to the Diablo, including the use of the elliptical coils and an operating frequency of about 20,000 hertz.The Lobo is the first detector using elliptical coils to have a true discrimination mode of operation. This discrimination circuitry significantly increases the versatility of this gold-hunting detector. When nugget hunting, this feature can reduce the number of targets that should be investigated. Also, with the discrimination feature, the Lobo makes an excellent coin-hunting instrument.To further increase the versatility of the Lobo, Tesoro has introduced a new line of wide-scan elliptical coils. With their addition, Tesoro now offers a total of six elliptical searchcoils that can be used on either the Lobo or the Diablo. There are three different sizes: a 7-inch, a 10-inch, and a 15-inch coil in either the original concentric or the new wide-scan design.FEATURES AND CONTROLSThe Lobo is also Tesoro's first detector to use their sleek new plastic control housing. Like many other Tesoro models, this new design has a quick and easy-to-use hip mount arrangement. Other standard features of the Lobo are an all-fiberglass lower rod and a 10-inch elliptical search coil. The control housing has a total of six controls, five on the front panel and one located at the rear. All five front controls are easily adjustable with the hand holding the detector. This makes any changes of modes, sensitivity, or discrimination level very convenient.The controls included are the following:1.    A 10-turn Ground Adjust Control2.    A three-position Mode Switch that selects the all-metal mode, discrimination mode, or retune the detector to the normal thresh-hold level3.    A three-position Auto-tune/Mode Change Switch is labeled as follows: Top position auto/all met; Middle position auto/disc; Lower position norm/disc The top two positions allow the operator to select a fast autotune while the lower position has a very slow autotune feature.4.    An On/Off/Sensitivity Control (The detector audibly checks the eight AA batteries when first turned on)5.    A Discrimination Level Control6.    A Threshold Control (located on the back of the plastic housing). FIRST IMPRESSIONWith all Tesoro instruments, the Lobo came packed with plenty of protection from possible damage in shipment. Because I planned to test the nugget-hunting capabilities of the Lobo in a very rocky section of the Arizona Mountains, Tesoro included their optional 7-inch concentric searchcoil. (I strongly recommend this size-optional coil for nugget hunting in rocky locations.)The assembly of the unit was quick and simple. The trick to installing the stem in the coils mounting tabs is to moisten the outer surface of the rubber inserts located in the stem. This allows everything to slide together easily.The next step was to take time to read the instruction manual, a step I recommend with any new detector. The manual is brief, but does a more-than-adequate job of explaining the operations of the controls, initial setup, and use by a beginner.CONTROLLED TESTINGThe Lobo I received from Tesoro was one of the first production models. Before I left for Arizona, I ran the detector through several tests to see how it would perform. After returning from Arizona, Tesoro informed me that improvements had been made to the discrimination circuitry. At Tesoro’s request, I sent the unit back to the factory for updating.Because the three minor changes are now standard on production models, I retested the detector using the same procedures as I had initially. Although Tesoro informed me the changes made a significant improvement, I wanted to see for myself.The results were so significant that I have included only the updated detector’s analysis. As before, I selected my front yard for my controlled test site and my initial tests were repeated.First, I placed a small 3-1/2-grain gold nugget (about matchhead in size) and two different types of hot rocks on the ground. The hot rocks were selected because they are a common problem in many gold-producing areas. The initial adjustments included the sensitivity set at maximum and the threshold set for a slight audio tone.The next step was to adjust the ground balance for minimum variation when I raised or lowered the searchcoil to the ground. Although the Lobo can be ground balanced in either the fast or slow autotone mode, I preferred to make the initial adjustment in the slow normal/disc mode. Once I had the detector properly ground balanced, I switched to the fast autotune mode and made minor adjustments as necessary.One characteristic I liked about the Lobo was the smoothness of all the signals. Even the updated model was surprisingly quiet with no pops and cracks common to extremely sensitive detectors. One feature of the Lobo I found somewhat concerning was the audio tone and maximum output when not using earphones. In noisy environments, I found the audio output somewhat weak, but since I always use earphones, this didn’t present a major problem for me.With the detector in the all-metal mode, I began testing the detector’s response to the gold nugget and the hot rocks. The Lobo detected the gold nugget with ease. Next I checked the two hot rocks. The Lobo gave the usual negative indication (the detector went quiet) over the magnetite hot rock and a positive indication over the reddish-brown piece of hematite. Both of the signals from the rocks were normal.I tried the discrimination mode next. With the discrimination level set at 0, I checked the hot rocks and the nugget for a response. This time the detector only responded to the small piece of gold. There was no signal from either hot rock. (In Arizona, I found this procedure easily identified the positive-sounding hot rocks.)The next part of the test was to see how the improved Lobo would perform against the tough Colorado soil by searching for the coins buried in my yard. Again selecting the all-metal mode, I found that the detector easily located most of the coins with a good strong signal. The Lobo also gave a respectable audio signal on my favorite target, a 6-1/2-inch-deep dime.Switching to the discriminate mode, I found the factory changes had made a significant improvement. With the detector properly ground balanced, the Lobo gave a good strong signal on most of the coins. The detector also gave a respectable signal on the 6-1/2-inch-deep dime. The above tests were repeated using the optional seven-inch elliptical coil and all responses were remarkably similar. As expected, the little nugget gave a better audio response in both the all-metal and the discriminate mode. Checking the buried coins I found the Lobo capable of detecting all of them, including the deep dime.The improvements in the discrimination circuitry definitely improved the detector’s response. These changes, however, make the adjustment of the ground-balance control more critical. The reason is because the discrimination mode uses a signal from the all-metal mode in its analysis of a target. If the ground-balance adjustment made in the all-metal mode is incorrect, either a loss in depth or excessive false signals while operating in the discriminate mode are possible.When the ground-balance is adjusted so the detector gets quieter when the searchcoil is lowered to the ground, the discrimination mode may give false signals when the coil is swept over the ground. If the ground-balance adjustment is set so the audio gets louder when the searchcoil is lowered to the ground, some of the deepest targets may be ignored.This is not a flaw in the detector. Tesoro has given this critical adjustment back to the operator. A beginning treasure hunter may find this condition a little confusing at first, but the professional wanting maximum depth in the discrimination mode will welcome it.NUGGET HUNTING IN ARIZONAMy previous nugget hunting excursions to Arizona have only yielded the 3-1/2-grain nugget mentioned above. This year, like last year, was going to be a family trip. All the way to Arizona, I was thinking of how I would write an article if I found nothing at all. Treasure hunters familiar with nugget hunting know it is possible to go for days and even weeks without finding a single nugget.We arrived at the selected site on the morning of December 31. It didn’t take but a few minutes of unpacking the detectors, digging tools, and other equipment and everybody was off searching. My standard setup of the Lobo was as follows: the sensitivity set at maximum, the discrimination level at minimum, and the mode switch set to fast autotune. The all-metal mode was selected as my standard mode of operation.After only a couple of minutes of searching, I realized that nothing had changed since last year. There were hot rocks everywhere and, every few feet, the soil mineralization changed dramatically. The smoothness of the audio tone that I had noticed at home was replaced by varying slight continually changing signal. The autotune was tracking the multitude of variations in the soil and rocks. Because of the extreme variations in the soil mineralization, I found I was periodically adjusting the ground-balance control.Although this might seem annoying to a beginner, the adjustment was usually minor and only took a couple of seconds to do. Once I was accustomed to the varying conditions, the adjustments became almost automatic in nature.The morning went quickly, but not without at least some benefits. I dug all targets and found that all the positive hot rocks could be easily determined by using the discrimination mode. This mode made almost all of the small iron trash, such as nails and pieces of cans, easily recognizable also. If the object gave a reasonable signal in the all-metal mode and was rejected in the discriminate mode, I was sure that it was a hot rock, a nail, or some other piece of trash.My first signal that gave a definite positive sound in both modes caused my heart to skip a beat. Unfortunately, it turned out be a small piece of lead, about one-half the size of the lead in a 22-caliber bullet. Soon after, lead became a common find. By lunchtime, I had accumulated quite a handful of junk. Because of the discrimination circuitry of the Lobo, I knew that most of these items were worthless before they were dug. But, as part of my testing procedure, I had decided to dig all targets.After lunch I began searching again. About 10 feet from where I ate, I received a strong signal. Checking the target again in the discrimination mode also gave a good, positive sound. By the size of the target and its close proximity to the road, I suspected the target to be a pull-tab. Boy was I in for a surprise.What was giving the strong signal was a heavy lump covered with red clay. A little rubbing yielded the glint of gold. I had just found my first decent-sized gold nugget! Needless to say I let out a loud yelp, alerting my brother-in-law. In a couple of seconds he was over admiring my find, a nugget weighing over a quarter-ounce. This nugget turned out to be the only good find in the area for the day.By the second day I could see the definite advantage to the thin elliptical-coil design. It was easy to poke the coil into tight places and under large boulders. With the Lobo equipped with the small coil, searching along the sides of hills, in ruts, and other strange places was fun. Although the little coil seemed heavy for its size, I found the constant manipulation of the detector over the rough terrain was not tiring. Searching the better part of the second day yielded a handful of trash, including two small lead shot guessed to be about #6-size shot. The Lobo had proved its ability to find extremely small targets.Late in the afternoon of the second day I was searching a streambed when I received a signal that gave a positive response in both modes. Searching through the gravel yielded my second heart-stopper - a nice, small gold nugget. Two nuggets in two days! I couldn’t believe my luck.The weather prevented any hunting the third day, but we were back at it again the following day. The fourth day passed quickly and I was about to quit when I got an ear-blaster of a signal over a crack in a large rock. Prying the rock apart yielded my biggest nugget, a triangular-shaped piece of gold that weighed almost a half-ounce! Three nuggets in four days! I was beginning to wonder if even I would believe my article.Part of the fifth day of our trip was used to gain access to a nearby ghost town. Once I obtained permission, I began to search the site. Unfortunately my heart wasn’t in searching for old coins when I could be searching for gold nuggets. The Lobo was equipped with the optional seven-inch coil that seemed to work exceptionally well among the typical trash of an old town site.Operating in the discrimination mode, the Lobo rejected most of the rusty-iron trash items. The old bottle tops would give an occasional good signal, but I found almost all of them would respond as trash when I slowed the sweep speed of the searchcoil over the object on additional passes. Unfortunately, the only non-ferrous items found were small pieces of copper wire, an occasional pull-tab, and miscellaneous copper and brass brads and buttons.The brief excursion in the ghost town displayed that the detector did a very good job of accepting non-ferrous targets while rejecting the usual iron trash found in a ghost town.I spent the last day of our detecting expedition in Arizona really concentrating on finding a small nugget. I was wondering just how small of a nugget I could find. After about three hours of hunting I got a very weak, but positive signal. The next several minutes were spent trying to find the little devil. Finally, I isolated the target, a tiny nugget about half a paper match head in size (1-1/2 grains in weight). Although it wasn’t the smallest nugget the detector can detect, the little piece of gold did display the Lobo’s capabilities.Out of the six nuggets found in the immediate area the week I spent in Arizona, I had found four with the Tesoro Lobo. While I was hunting the ghost town, my brother-in-law was fortunate to find one of the other nuggets. The sixth nugget found in the area was found by Gene Walthall, a fellow nugget hunter from Utah. Gene was using a Tesoro Diablo at the time of the find.By the end of the week, I was convinced that the best way to hunt gold nuggets was with a detector developed for that purpose. I also found the small, thin elliptical coil worked exceptionally well under the adverse rocky conditions. More importantly, I had four nuggets that together weighed over 3/4 of an ounce to verify the Tesoro Lobos capabilities.CONCLUSIONThe Tesoro Lobo is a truly functional gold-seeking detector capable of finding the smallest of nuggets. With the improvements to the discrimination circuitry, this detector also proved to be one of the more sensitive detectors I have used for coin hunting.The narrow footprint of the elliptical coil makes this detector an excellent choice. This coil design has several advantages over the standard round coil. Because of its design, this slim coil could slide into very tight places, cracks, and other narrow openings where standard round coils couldn’t fit.I found this detector to be one Tesoros best instruments for versatility and sensitivity. I wouldn’t be a bit bashful in recommending this detector to anyone who is looking for a detector that can be used for almost any type of treasure hunting.

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