Jump to content

Search the Community

Showing results for tags 'fisher detector'.

More search options

  • Search By Tags

    Type tags separated by commas.
  • Search By Author

Content Type


  • Metal Detecting & Gold Prospecting Forums
    • Meet & Greet
    • Detector Prospector Forum
    • Metal Detecting For Coins & Relics
    • Metal Detecting For Jewelry
    • Metal Detecting For Meteorites
    • Gold Panning, Sluicing, Dredging, Drywashing, Etc
    • Rocks, Minerals, Gems & Geology
    • Metal Detector Advice & Comparisons
    • Metal Detecting & Prospecting Classifieds
    • Compass, D-Tex, Tesoro, Etc.
    • First Texas - Bounty Hunter, Fisher & Teknetics
    • Garrett Metal Detectors
    • Minelab Metal Detectors
    • Nokta / Makro Metal Detectors
    • Tarsacci Metal Detectors
    • White's Metal Detectors
    • XP Metal Detectors


  • Best of Forums
  • Gold Prospecting
  • Steve's Guides
  • Steve's Mining Journal
  • Steve's Reviews


  • Free Books
  • Bounty Hunter
  • Fisher Labs
  • Garrett Electronics
  • Keene Engineering
  • Minelab Electronics
  • Miscellaneous
  • Nokta/Makro
  • Teknetics
  • Tesoro Electronics
  • White's Electronics
  • XP Metal Detectors
  • Metal Detector Settings

Find results in...

Find results that contain...

Date Created

  • Start


Last Updated

  • Start


Filter by number of...


  • Start



Website URL










Gear Used:

Found 46 results

  1. I've been discussing qualities of Minelab lately (mostly in a negative light) and I decided to step back and ask myself why I use their Equinox 800 almost exclusively. It's worth starting out by saying I'm an old coin hunter (where 'old' is meant to refer to 'coin', although it also applies to 'hunter' 😁) the majority of the time, and and native gold hunter when the opportunity presents itself (not often enough). I've never detected near salt water and only occasionally (in shallow creeks) detected in water. Relics and jewerly aren't ignored but they typically only show up when I'm coin hunting, as peripheral bonuses. I want to emphasize from the beginning that I'm not reviewing/comparing these two for all conditions or even conditions that might apply to the average detectorist. This is all about me, well, about my conditions, particularly my hunting preferences/goals. Although that may seem selfish/uninteresting/unapplicable to readers here, in the least it might get you thinking about how different detectors 'weigh in' for your type of detecting. A Minelab GPX 5000 might be well worth the cost and backbreaking swings for someone, but if it doesn't fit your intended targets and locations then you wasted a couple thousand $ and may not even be maximizing your intended finds. I'll put some more caveats at the end, but basically I've broken this into three parts. The first are some quantitative/qualitative properties that are easily measured/stated. Next are the less quantifiable features/performances that mean the most to me. 3rd I list qualities that I determine are important but for which I don't see a significant advantage for either model based upon my usage. And finally I'll mention some of the things which most comparisons emphasize but for which I don't because..., well, you can read the reasons I give then. For completeness, the Fisher F75 is a 13 kHz single frequency IB/VLF detector whose initial model was released 11-12 years ago. Although I own the F75 limited (Black), I'm instead comparing the F75 plus since it has all the features I use at a lower price. The Minelab Equinox, both a simultaneous multifrequency and selectable multifrquency (5 kHz to 40 kHz) was released early 2018 with two models which continue to be the only ones available. The 800 model has more features. That is the one I own and compare here. One final clarification: in the second section, '++' means a feature/performance which is very important to me, and '+' means important, but less so. I emphasize 'to me'. That is, it might be a small or meaningless difference to many but it matters a lot to me. I suspect many of you have noticed I haven't included such fundamental features as waterproof/submersible and multifrequency/single frequency. The former is because it doesn't affect my hunting requirements. The latter is a bit more complicated. Rather than mentioning operating frequencies, I chose to emphasize the performance features. I don't really care what frequency/frequencies are being used as long as the detector performs (or outperforms) in the categories that matter to me. For example, simultaneous multifrequency improves the accuracy of the TID for deep/weak targets. The Eqx 800 got a ++ there. It should be clear that in the center section, which IMO is the most important, the Eqx 800 clearly outperformed the F75. My preference for the Eqx 800 as my primary and the F75 as my backup is thus justified. Update 1: based upon some questions that follow in this thread, I will do more detailed depth test comparisons to clarify my claim that F75 has more raw depth. I'll report those results in this thread as soon as I finish and will put another update on this post to call attention to it. Update 2: I've done a detailed hybrid (in-ground + air above ground) depth test in my test garden and those results can be found later in this thread. As such I've removed the 'raw depth' line in the above table since it's been superceded in much greater detail in the later post. If interested you should read that.
  2. This is a prototype machine I acquired from Tom Dankowski many years ago. It looks just like any other 1270, until you examine the serial tag. This is a prototype that the old Los Banos Fisher had made to experiment with aluminum discrimination. The IRON disc is actually a “segmented” ALUMINUM disc that you can adjust with laser like accuracy. For example: Imagine you have your whole band of disc, from iron to silver, and you now place a magnifying glass over the aluminum portion of the disc. Now, if you are at a site that has an excessive amount of one certain kind of pull-tab, like a new style lift top, you can now disc it out and dig just the older style pull-tabs. You can also, eliminate most pull-tabs and dig nickels and all gold in that nickel range, tipping the odds in your favor to find more mid to large size gold rings without having to dig all pull-tabs.
  3. I have the Fisher F75+. If I have the discrim set at say 30, why do I sometimes get low VDI numbers like 6 or 7?
  4. Occasionally in posts I see reference to mineralization and how it affects detector performance. It is often vague with usage of words like 'mild, moderate, severe'. In fact several detectors have the capability of measuring it. Two of mine -- Fisher Gold Bug Pro and Fisher F75 -- have that capability. Until now I've typically paid little attention to it. (Magnetite) mineralization and its effects are clearly important in many detecting for native gold situations, but it's also meaningful for other forms of detecting, if nothing else when comparing notes on detector performance. Extreme cases we've seen are Tom Dankowski's reports on the depth he gets in the sandy, non-mineralized soils of Florida vs. Steve Herschbach's difficult Reno parks. An even more extreme example has been reported multiple times by Mark Gillispie in coal ash laden school yards. Here are the pertinent sections from the F75 and F19 (Gold Bug family member) user manuals respectively regarding the meanings of their magetite measurements: Personally I prefer the F75 readout since it quantifies the meaning of the bar levels. Not sure why the Gold Bug scale wasn't equivalently defined, maybe another example of "don't step on the toes of the more expensive model" syndrome.... Yesterday I made measurements in my back yard with both detectors, two coils each (stock Fisher 5" round DD and 7"x11" DD). In all cases I ground balanced before taking the measurements. For the F75 the ground phase values in my backyard as a whole were 61 with its 5" coil and 64 with the 7"x11" coil. In those locations (still F75) the 5" showed 2 bars and the 7"x11" was about 50-50 divided by 2 bars and 3 bars. The measurements made with the Gold Bug were nearly identical in terms of the bars shown (2 with 5" and 2-->3 with 7"x11") for ground phases of ~64.5 and ~60 respectively) even though the scales on the two detectors don't really align in terms of the units of measure. Now here's a possibly interesting and serendipitous observation: for my teststand the readings were 3 bars in three of the four cases (I missed the measurement with the GB Pro and 7"x11" coil). If you refer back to the linked thread there is a drawing which shows a concrete layer at 15" depth. This was made with a store bought bag of concrete mix. Those contain not only the cement but also sand and gravel filler. Where did that sand and gravel come from? I don't know but it sure appears that it came from a site more mineralized than my back yard! I vaguely recall previous measurements I've made (but failed to record -- my bad) in my back yard where the F75 read 4 bars. One thing I wonder about is how much soil moisture affects the measruement. (We haven't had rain for a couple weeks so the ground is considerably drier than typical for the late autumn, winter, early spring months here when I likely took those earlier measurements.) But there are other variables so I wouldn't conclude that moisture does have an effect. One would hope not, but certainly dectectors are known to perform differently when detecting in various soil moisture conditions which is why I wonder. As always I'd be interested in seeing other measurements (regardless of detector model) and comments.
  5. Steve I plan on going civil war relic hunting this weekend in an area of a lot of action including cannon balls. I’ve read online how to put it in all metal mode, but step by step or whatever, would all metal be better than BP?
  6. This is less of a comparison and more of a question. It is a real head scratcher for me. I am not in any way trying to put down one detector and hype up another. This is just my experience. So, I recently had another try at the F75/T2/F70 platform. I have over 150 hours on these detectors and have now sold them all.......Why? My last go at this great group of detectors was with a 2016 F75LTD Special Edition with all of the latest features. After ten outings with it (about 40 hours) I have given up. Selling on Ebay right now with bids. My last work with it was at a city park that has such bad EMI that a Version 4 Omega 8000 and a T2+ were unusable there. This newer F75LTD had no audible issues with EMI at this park which for me anyway was a big improvement. My problem with it was determining a dig or not dig signal. At this park there is an audible signal every 2 or 3 inches, sometimes even closer. I did two field tests with the F75LTD 11"X7"DD and an Equinox 600 11" DD. Settings for the F75 were ground balance 87, Fe3O4 4 to 5 bars, DE mode, discrimination 15, 4 tones, sensitivity 80. Settings for the Nox 600 were ground balance 3, default Park 1 except for a bit of threshold tone set at 6 and sensitivity at 17 (even the Equinox can have EMI issues). I did use the horseshoe button a lot for iron ID. The first time I did this field test I did not want to believe the results. They were not pretty and were basically repeated in this second field test. So, I decided to try again. Both times I picked an area about 50 yards long and 2 yards wide, roughly a full sweep in one direction/lane and a return to the beginning in the adjacent lane. I marked the area off so I wouldn't stray or miss any ground. First I used the F75. Tons of signals, 1/4" aluminum shards are everywhere from shredded pop cans...... came up with 41 cents (3 clad dimes, 7 zinc pennies, 4 pre-1982 copper pennies) , a really cool HO scale tractor (I am a model train guy too, so great find, don't even have to weather it!) a shell casing and some pull tabs, etc. I did hit a really big target that sounded like big iron falsing by itself and did not dig it. There were so many iffy signals (at least to my ears and eyes with numbers and tones all over the place). I was only concentrating on two-way signals with generally consistent numbers and those are the targets I recovered. None were more than 6" deep. Next I covered the exact same ground with the Equinox. From the photos you can see that I or the F75LTD or a combination of both missed a lot of legitimate targets. It was easy to make the dig or no dig decision on these targets with the Nox 600. They were solid, two way, stable numbers and audio, no brainers. None were more than 8" deep and most were in the 2" to 4" range. The big iron screw had a clad dime that was 1" away from it and a little deeper than the top of the screw which was 3" below the surface. I heard the clad dime clearly both during sweeps and pinpointing, two separate obvious.targets. Lots of silver mercury dimes and wheat pennies in this area so I dug both targets. I only heard the iron with the F75. Also, there is no way using the Nox 600 that I would have missed the vast majority of the targets that I recoverd earlier with the F75. They were not difficult targets to recover. Also, except for the big iron screw and dime, I did not dig any targets with the Equinox 600 that were in previous F75 plugs or even adjacent to them, like within masking distance unless the F75 with the settings I was using can have masking issues with targets 4" apart........... So, I guess I am super spoiled by the Equinox.......or I seriously suck at the F75/T2 platform. Jeff These were recovered by the F75LTD These were recovered in the exact same ground afterwards by the Equinox 600. 1974 Kennedy half dollar, 1983 Washington quarter, 3 clad dimes 9 zinc pennies, 6 pre-1982 Memorial pennies, several pieces of lead and solid aluminum, etc.
  7. People often forget about factory reset functions since it is still a rare feature. I am a proponent of resetting newer generation digital metal detectors on a regular basis, especially if settings get changed around a lot. The more setting changes are made, the more chance of a programming bug slipping in and messing with the operator. This is the procedure for the many F75 variants out there. From the F75 Owner's Manual page 10: RESET function The F75’s microprocessor saves all settings which you input, even after the power is turned off. If you wish to reset the settings to the factory preset, follow this process: Turn detector off. Press-and-hold the red MENU button and push-forward-and-hold the TOGGLE SWITCH. Turn the detector on, while you are still holding the controls. Release the MENU button and TOGGLE SWITCH. See the F symbol. When the F disappears, the detector is reset. Note: some latest F75 versions may show five pairs of number instead before displaying the F - the ten digit serial number. All settings have now been returned to factory defaults. Fisher F75 Metal Detector
  8. Hi all, I'm new here. I really like this site with all the great advice. I read Steve's detector reviews. Excellent stuff... I'm new to metal detecting and would really like to get into it. I'm foremost interested in nugget hunting, but also general detecting in the parks and on the beach. After reading all the reviews here I'm thinking of getting a Fisher F75 LTD. I'm a fairly tech savvy person, and learn pretty quick. I'd rather spend more in the beginning and have a good machine to grow into. But I read some opinions that the F75 might be too much machine for a beginner. So I'm asking the experts here if I'm better off with a Fisher Gold Bug Pro or a Fisher F19. I would welcome some input. Thanks! Herb
  9. Version 040113 Rev 3

    1 download

    Fisher F75 Operating Manual, 3.25 MB pdf file, 44 pages Fisher F75 Data & Reviews Fisher F75 - Steve's Review First Texas (Fisher) Forum
  10. Version 110614 Rev 5


    Fisher F75 Special Edition DST | F75+ User's Manual, 5.06 MB pdf file, 48 pages Note there is some confusion regarding the Special Edition (Black) as generally being referred to as Limited or Ltd models in most advertising since the Special Edition is just a color version of the Limited. The Fisher F75+ is also another version of this same detector, sold with different accessories. Fisher F75 Ltd (Special Edition) Data & Reviews Fisher F75+ Data & Reviews Fisher F75 - Steve's Review First Texas (Fisher) ForumFisher F75 - Steve's Review
  11. Version 103012 Rev 3


    Fisher F75 Limited Camo Users Manual, 2.96 MB pdf file, 48 pages Fisher F75 Ltd Data & Reviews Fisher F75 - Steve's Review First Texas (Fisher) Forum
  12. Version 032513 Rev 3


    Fisher F75 Special Edition Black Users Manual, 4.38 MB pdf file, 48 pages Fisher F75 SE Data & Reviews Fisher F75 - Steve's Review First Texas (Fisher) Forum
  13. Version 110614 Rev 5


    Fisher F75 DST Users Manual, 4.73 MB pdf file, 44 pages Fisher F75 Data & Reviews Fisher F75 - Steve's Review First Texas (Fisher) Forum
  14. I am collecting manufacturer catalogs and user guides into the Downloads section of the website. I am building a Metal Detector Database and want to be able to link to manuals that stay in permanent locations. It also makes it easier for members to find manuals from various sources all in one place. I was unable to find reader versions of the manuals for the Fisher F75 DST, Fisher F75 Ltd DST, and Fisher F75+. The versions available online are set up for printing and the pages are out of order for reading on electronic devices. I carry all my manuals on my phone or iPad these days, and so reader versions are more useful for me and I suspect also for others. So I took the time to reorder these documents into reader forms for download. The pdf reader version of the basic F75 with DST can be downloaded here. The pdf reader version of the F75 Ltd with DST and F75+ (they are the same detector) can be downloaded here. All the Fisher manuals and catalogs I have uploaded so far can be found here. I am adding models daily.
  15. Hi Simon… I realize that your T2 is somewhat different from the F75. But let me describe how I operate the original F75 to deal with issues related to EMI. The original F75 version is very much subject to erratic behavior in areas where EMI is present. Hunting urban areas in zero discrimination with the stock 11” DD coil is frequently impossible. I avoid using this coil in urban environs because it is quite vulnerable to EMI issues (extra windings / antennae effect) compared to the 10” elliptical concentric coil, and this is especially true when compared to any of the smaller coils. So don’t hesitate to switch to a smaller coil, preferably a concentric coil if the ground conditions permit. An added benefit if hunting micro jewelry, is that the smaller coils, particularly the 6” elliptical concentric coil, is quite sensitive to small stuff compared to the stock 11” DD coil. In fact I put it to good use for hunting naturally occurring native silver in rocky environs. It’s not unusual to find sub-grain material with this coil. If using a discriminate mode, avoid JE mode in EMI areas. It is extremely high gain, and therefore much more sensitive to EMI than are the DE or PF search modes. Another very useful technique, if necessary, is to increase the iron discrimination level until erratic behavior settles down to an acceptable level. Do this while moving / holding the coil on the ground, and not while waving it around in the air. Keeping the coil to the ground much reduces EMI instability because it reduces the coil’s antennae effect. Adjusting the sensitivity control is not necessarily the final step in stabilizing how the machine behaves in EMI environments. Do as you please with it. Keep in mind that you may wish to limit iron discrimination to about 6 or 7 and no more as Steve describes, depending on your preference. At that point, if necessary, you may wish to experiment with decreasing the sensitivity control to achieve stability. Of course for prospecting applications, and low trash urban areas, the first choice is to search in the motion all-metal mode. It is much less vulnerable to EMI than are any of the discriminate modes. It makes a huge difference. In closing, I should add that in remote prospecting areas, my original F75 is normally as quiet as a churchmouse regardless which search mode, settings employed, or the type / size of coil that is used. On rare occasion we do experience an intermittent EMI induced instability from what I suspect is the local microwave tower. These occasions are always temporary, rarely lasting more than a half-hour…………….. Jim.
  16. Once upon a time all metal detectors went beep, and you dug up a metal object. Then a simple form of discrimination was developed based roughly on the conductivity scale. The main feature of this scale is that ferrous (iron or steel) items read lower on the scale than non-ferrous items. In a perfect world all ferrous readings could be set as a negative number, and all non-ferrous items set as a positive number. The reality is not so perfect however. Some steel items, especially items with a hole like a steel washer, will read up in the middle or high end of the scale, and show up right where only non-ferrous readings should appear. Thin sheet steel (bottle caps, flat section of rusted cans or roofing material) can show up in the mid range, and hardened steel items like bolts or ax heads can read way up in the silver range. These types of targets can trouble coin hunters in particular. Gold reads much lower on the discrimination scale normally due to a fairly low conductivity for gold. The gold range overlaps entirely with the lead and aluminum ranges, and these items are arranged on the scale based more on size than anything. Small gold, aluminum, and lead reads very low, and larger gold, aluminum, and lead tends to read in the low to middle portion of the scale. Those who chase these low end targets run into another problem with ferrous. Very small gold, lead, aluminum, and other small non-ferrous low conductors actually overlap with small ferrous items and so the clean ferrous to non-ferrous "breakpoint" does not actually exist,. The breakpoint is more of a "breakzone" i.e. a fuzzy zone where items overlap. The ground itself contains ferrous materials in the form of iron minerals. Ground minerals can act to confuse the detector further, enhancing the chance that a small non-ferrous reading will be interpreted as ferrous. Another way to say that is that in highly mineralized ground the overlap between ferrous and non-ferrous targets gets larger. The ground mineralization is critical to how this all works and so air testing is not recommended for testing the ferrous/non-ferrous overlap region on any particular detector. Note that this does not apply just to very small items. The deeper an item is, the smaller it appears to a detector. In other words a deep large item can sound just like a shallow small item. When you bury items of any size in highly iron mineralized ground, the deeper they are, the more chance the ground mineral signal will overlap and cause the item to read as ferrous right at the edge of detection range. Fisher F75 metal detector The early model discrimination detectors usually had a knob that adjusted all the discrimination. Everything below the knob setting was ignored, and everything above the setting accepted. The discrimination pioneers rapidly discovered that the dividing line between ferrous and non-ferrous is "fuzzy". The knobs could be set to reject nearly all ferrous readings, but then some good non-ferrous targets would get missed. The solution was to use a little bit lower discrimination setting, which meant more ferrous trash was dug, but more non-ferrous items were revealed. Managing the ferrous to non-ferrous breakpoint is critical. There is no setting that rejects all ferrous while detecting all non-ferrous, and the more mineralized the ground is, the less reliable the settings become. As a rule of thumb, the more aggressive the iron rejection, the more chance of non-ferrous items being misidentified. Detector technology advanced, and tone schemes were developed that divide the discrimination scale up into segments or "bins" where all numbers within a specific range make a specific tone. These tone schemes are often preset at the factory. The ranges can be arbitrary and arranged in many ways, but all share one common factor. Where is the setting that divides low ferrous tones from the higher non-ferrous tones? This is the "ferrous breakpoint". Everything below this point will give a "ferrous tone" and everything higher a "non-ferrous tone". The detector engineers are well aware of the overlap between ferrous and non-ferrous items. In choosing one setting to define what is in reality a zone the engineers have to make a hard choice. If the setting is too low, the operator will get many non-ferrous readings that turn out to be ferrous. That really irritates people. Or they can set the breakpoint higher. That way less ferrous gets dug. Some good non-ferrous items will also be missed, but only in the rarest cases does anyone ever know what they are missing. The odds are there will be more complaints if the ferrous breakpoint is too low than too high. The goal is not to find every non-ferrous item, but to keep from digging too much trash identified as good. This diagram is shows the common discrimination range employed in nearly all metal detectors. This particular model (Garrett) sets 40 as the point where ferrous items separate from non-ferrous items. Yet the chart reveals the overlap zone runs from about 35 to 45, a solid ten point spread. Small gold can identify as ferrous, especially in iron mineralized ground. Many detectors identify this zone on the meter via overlapping diagonal lines. The ferrous/non-ferrous overlap region What this means is that any detector that employs a preset tone scheme with no ability to adjust the "ferrous tone breakpoint" is assured to be missing at least some items due to an overly aggressive setting dialed in at the factory. This was eventually recognized, and now quite a few detectors allow the point where ferrous tones flip to non-ferrous tones to be adjusted. Some models are now even allowing for multiple volume controls for each separate tone, are at least the ferrous tone. This is most often called a "ferrous volume" setting. The Fisher F75 is an earlier tone based model and as such the tone schemes are preset at the factory. You can choose between the schemes, but the tone settings of where the tones occur cannot be adjusted. The F75 employs a target id scale that ranges from 1 to 99 with the 0 - 15 range defined as ferrous. From the F75 Users Manual page 20: 1. 1-7 iron 2. 8-15 iron 3. 16-20 foil 4. 21-25 foil 5. 26-30 nickel 6. 31-35 nickel 7. 36-45 tab 8. 46-55 tab 9. 56-60 zinc 10. 61-65 zinc and from page 25: F75 OBJECT AND TARGET I.D. Most iron objects 4-12 foil from gum wrapper 16-25 U.S. nickel (5¢ coin) typically 30 aluminum pull-tab 33-55 aluminum screw cap 60 - 70 zinc penny (dated after 1982) typically 60 aluminum soda pop can most often 63-69, but can vary widely copper penny, clad dime typically 70 U.S. quarter (25¢ coin), clad typically 80 50¢ coin, modern clad typically 86 old silver dollar coin typically 90 US silver Eagle $1 coin typically 91 The implication is that non-ferrous items will only read 16 and above. Any readings of 15 and lower are deemed ferrous. The F75 has several preset tone schemes, the basics being monotone, two tone, three tone, four tone, and Delta Pitch (separate tone for each target id number i.e. multitone). The quirk is simple. The two, three, and four tone schemes all have a non-adjustable factory preset low tone for ferrous at 15 and below. The tone schemes override any other discriminations settings. In other words, if you have manually set the discrimination for ferrous to be a lower setting, switching to any two, three, or four tone scheme will automatically change the low tone setting to be at 15 and lower. The problem is that with time it was revealed that the F75 will detect some non-ferrous items at much lower settings than 16. Tom Dankowski finally put it all together and determined that a reading of 7 or higher would reveal additional non-ferrous items that are rejected when the setting is at 15. Tom's recommendation for the F75 while hunting ferrous is therefore to not use the tones, but to use the monotone setting and adjust the discrimination manually to 6. That way items 7 and higher signal as a non-ferrous target instead of delivering a low ferrous tone via the tone schemes. Again, going to a tone setting will automatically override a manual discrimination setting if one has been set. Tom wrote this all up as a great article in the 2009 Fisher Labs World Treasure News on page 11. I actually had the chance to see this in person in my own use of the F75. Early on I trusted the tone settings and two tone is quite handy for those simply wanting to dig all non-ferrous. Yet on my trip to England with the F75 I encountered a mystery. A gold coin was found and another F75 newbie was telling me about how he tested it with his F75 and it gave a nice ferrous tone. He was quite upset and worried his detector was defective. He did not have the coin however and so I could not see what he was describing and at the time I have to admit I was clueless. I know now that he was using tones, and that the gold coin was reading lower than 16 and so being identified as ferrous! My early use of the F75 was more for gold nuggets, and I usually used all metal mode. Yet my favorite feature on the F75 was full time target id while in all metal mode. My method was to acquire all targets, then dig any that flickered even once above my mental ferrous breakpoint. Unfortunately I leaned too much on the user manual initially and tended to pass on targets reading under 16. My early writing on the subject reflected that. After I discovered on my own that gold was reading lower I started adjusting my mental settings lower. Then I bumped into Tom's writing on the subject and it all came together. The bottom line in that non-ferrous items can read as low as 7 on the F75 yet the ferrous tone break is set at 15. This is just fine for most Park coin detecting, but problematic for those hunting low conductors of any sort or coins in dense ferrous. Either use monotone and decide where you want the setting to be (6 as Tom recommends or maybe somewhere in between 6 and 15 if 6 has you digging too much trash) or hunt in all metal and use the target id numbers to decide when to dig keeping in mind non-ferrous can read lower than 16, especially in high mineral ground. This is not a flaw in the F75 but just a function of any detector using a preset tone scheme. There are many detectors like this on the market. They tend to be less expensive models, or older models, as most new detectors now feature an adjustable tone break for the ferrous/non-ferrous overlap zone. Another take on the subject. And down the rabbit hole - Tune Out Nails - You Will Miss Gold! Fisher F75 Information Page
  17. Benchtesting Rocks & Minerals with an F75 Metal Detector Introduction From the earliest time when we were aware of our surroundings, most of us looked for pretty rocks. We wondered what interesting or valuable minerals might possibly comprise them. Now as adult hobbyists, I doubt if any of us hasn’t benchtested an interesting rock from curiosity, and wondered what actually produced the signal. Although a sensitive benchtest usually has little in common with how marginally conductive rocks and minerals respond to metal detectors in the field due to ground effects, we can learn and become familiar with how rocks and minerals in our respective areas respond to metal detectors in a benchtest. A sensitive metal detector’s electromagnetic field penetrates rocks, usually generating either a positive or a negative signal in response to whatever material is in the rock. We can sometimes determine whether such signals should be investigated further, or whether worthless iron minerals produced them. I’d generally describe my benchtest results as worthwhile and informative, but that notwithstanding, I look forward to doing a benchtest because I think it is an intriguing study on its own merit. That said, how do you conduct a benchtest? I’ll describe my methods and hopefully we’ll see what you think about it. Benchtest Requirements and Techniques Benchtesting ideally requires a visually displayed, fully calibrated, manually adjustable ground balance that covers the entire (soil) mineral range from salt to ferrite. As a minimum, the detector should feature a threshold-based true motion all-metal mode, and preferably an additional true non-motion all-metal mode for significantly improved sensitivity to borderline samples. Visual displays in either of the true all-metal modes are essential for target ID, Fe3O4 magnetic susceptibility and GB readouts. I prefer a small (concentric) coil to promote detector stability and improve sensitivity to the rock sample, to ensure uniform sample exposure to the coil, and to minimize EMI (electromagnetic interference) especially if benchtesting at home. Elevate the sensitivity control as high as possible while maintaining reasonable detector stability such that you can clearly hear changes to the threshold. To check for a target ID, move the sample back and forth across the coil at a distance that produces the best signal but does not overload the coil. To determine ground balance and Fe3O4 readouts, advance the sample toward the coil, back and forth to within an inch or two (depending on sample size and signal strength) of the coil’s electrical sweetspot. Ensure your hand does not come within detection range of the coil to avoid creating false signals. If you extend your fingers to hold the sample, this is not an issue when testing larger samples. If necessary use a plastic or wood food holder that can firmly grasp small samples. Benchtests should be conducted utilizing a minimum of two widely diverse GB control adjustments. Initially I prefer the same GB control adjustment that is typically required to keep my detector ground-balanced to the substrates in my prospecting areas. It’s a personal preference that works for me. That particular GB control point (F75 / GB86) is more likely to improve any rock or mineral sample’s signal strength compared to using a more reduced (more conductive) GB compensation point. The next step is to use a dramatically reduced GB control adjustment (F75 / GB45) as suggested by Fisher Research Engineering. This setting ensures that (obviously weathered) oxidized samples do not generate a positive signal from any type of non-conductive iron mineral inclusions, particularly maghemite mineralization that may be present within such rocks. It follows that this second benchtest will, if anything, slightly subtract from the sample signal strength, particularly with low grade and otherwise marginally conductive samples, compared to the first step of the benchtest at GB86. As a general rule, I do not recommend the F75 / GB45 compensation point for benchtesting (non-oxidized) mafic samples that are dominated by constituents such as common magnetite or other black minerals that normally support highly (non-conductive) elevated GB readouts. Such samples can produce strong negative threshold responses at the reduced GB compensation point. It will be difficult or impossible for the signal from a marginally conductive substance to successfully compete with those negative threshold signals. For non-oxidized samples Fisher Research Engineering suggests using F75 / GB65 rather than the F75 / GB45 compensation point, since obvious iron mineral oxidation should visually be absent from such samples. With the above discussion in mind, extremely fine-grained, unweathered magnetite that occurs in pyroclastic material (for example volcanic ash) can drop into the GB45 range, but it is extremely rare. Unweathered volcanics do frequently drop into the GB70's due to submicron magnetite, but the recommended F75 / GB65 compensation point will eliminate those positive signals. The arsenopyrite sample depicted above is a good example of a commonplace mineral that we encounter in the silverfields of northeastern Ontario. Generally field examples could be described as marginally conductive and many are low-grade. A good many react with only a mild positive signal, and sometimes not at all to a benchtest depending on which GB compensation point is used. The high-grade, solidly structured sample above produces a strong positive signal in either zero discrimination or true motion all-metal mode with the ground balance control adjusted to the GB compensation point required for our moderately high mineralized soils. As noted, that’s approximately F75 / GB86, although in the field, of course, it varies somewhat depending on location and coil type / size employed. The response is not as strong as a similar size and shape metalliferous sample would produce, but it does generate a surprisingly strong benchtest signal that would be readily detectable in the field. Even with the GB control dramatically reduced to more conductive values (F75 / GB45), to ensure that any positive signals produced by non-conductive iron mineral inclusions should now only produce a negative threshold signal, it is no surprise that this (non-oxidized) specimen continues to generate a strong signal. For those readers unfamiliar with detector responses to such minerals, the same general response scenario described above with arsenopyrite applies to other marginally conductive minerals such as galena, pyrrhotite and to a lesser extent even iron pyrites. Ordinary iron pyrites is generally innocuous, but maghemitized pyrite, pyrrhotite, and the copper sulfide ores, particularly bornite and chalcocite, can be a real nuisance in the field due to magnetic susceptibility, magnetic viscosity, and / or electrical conductivity, just depending on what minerals are involved. Such variable responses from arsenopyrite and many other mineral and metalliferous examples clearly infer that signal strength and potential target ID depends on a sample’s physical and chemical characteristics, including the quantity of material within a given rock. These factors include structure, size, shape, purity (overall grade), and magnetic susceptible strength of iron mineral inclusions. Moreover, the VLF detector’s sensitivity, the GB compensation points employed, the coil type and size, and the sample profile presented to the coil further influence benchtest target signal strength and / or potential target ID readouts. Incidentally, neither of my PI units will respond to the arsenopyrite sample depicted above, even with a TDI Pro equipped with a small round 5” mono coil, the GB control turned off, and a 10 usec pulse delay to deliver its most sensitive detection capability. That result is typical of most, but certainly not all sulfides and arsenides that occur in my areas. Higher grade and solidly structured pyrrhotite, an unwelcome nuisance iron sulfide, and collectible niccolite, a nickel arsenide, are commonplace mineral occurrences here that do respond strongly to PI units, although their respective VLF target ID ranges are quite different. As a related but slight diversion, the photo below depicts a handsome example of the widely occurring mineral sphalerite. It forms in both sedimentary beds, and in low temperature ore veins. It is interesting to collectors because it possesses a dodecahedral cleavage which means that it breaks smoothly in twelve directions, and it is usually triboluminescent, meaning that it gives off a flash of light when struck sharply. Like many desirable minerals lurking in prospecting country, unfortunately sphalerite doesn’t react to metal detectors. A Final Word The foregoing is intended to illustrate that sensitive metal detectors can be utilized as a supplementary tool to assist with evaluating rocks and minerals. There is no question that the benchtest has serious limitations, particularly if trying to distinguish positive signals produced by some types of iron mineral inclusions from weak conductive signals. That notwithstanding, a positive signal that persists below the F75 / GB45 compensation point cannot be confused with iron mineral negative threshold signals produced at that same compensation point. Therefore a positive signal merits further investigation. Such signals are almost certain to be generated by a marginally conductive mineral or a metalliferous substance. On the more interpretive side of a benchtest, we need to point out that weak positive signals from lower-grade samples of minerals such as arsenopyrite, galena, pyrrhotite, chalcopyrite, and doubtless a few others, may disappear well before the GB control is reduced to the F75 / GB45 compensation point. We learn early that benchtests are frequently equivocal and require interpretation based on any further evidence that might support the benchtest result. Look for iron oxidation in addition to structural or other physical evidence as described above that could explain why a sample reacts as it does to a metal detector. Jim.
  18. Found this on eBay and confirmed that it is only 1 of 4 made. I know Russ B. Owns one. This guy stumbled in into his on the FB marketplace and then discovered how rare it is. I think the bottom line may be a bit ambitious, but who knows.
  19. Is anyone going to get the new Fisher F75 Plus? They sure put together a nice kit at a good price. thanks Bill
  20. I have a feeling it FT is about to rock the detector world, they have been too quiet for too long. They have some of if not the best detector engineers in the world, they have lowered prices on the F75/T2 platform to a level that is bringing them into the mid-level machine price range, even though they they are still at the top performance wise. FT is behind in the all terrain business but that wont last long and I think you will see a repackaged waterproof F75/T2 machine very soon and a true game changer shortly there after. I had an Equinox on pre-order but other than being waterproof (which I really don't need), my F75 LTD SE has more depth and is plenty fast for my hunting, thus I canceled my order. I am going to wait and see what FT has up their sleeve, until then I will keep going behind the latest and greatest machines and dig what they can't hear.
  21. (I moved the conversation over here since it was going off-topic.) In the above thread, relicmeister mentions that he put the Teknetics Omega ("frat brothers") 5in X 10in DD coil on his F75 and it worked fine. I expressed surprise and a motivation to try that out myself. I can now confirm that my Fisher Gold Bug 5"x10" DD works on my F75. I'm going to investigate further. I have both 5" round DD and 7"x11" DD for both these detectors. I'm curious to see if I can find any differences when mounted on the F75. Different ground balance numbers? Different TiD values? Different sensitivity (depth)? I also have an inductance meter so I'll make some measurements of the coils on the bench and see how different that important characteristic is. This might shed some light on why to swap works. Stay tuned.
  22. An acquaintance has asked if I'd help him find some shotguns he buried several years ago. They are wrapped in oilcloths, sealed in PVC pipes (~3 in = 7.5 cm diameter) and buried about 20 inches (half meter) deep according to him. He says he can show me the approximate location within about 10 m. If all this is accurate it seems like an easy task.... Then again, he also said someone in his family (without him being present) tried to find them with a detector and couldn't. That could be due to a lot of reasons as I'm sure you are already thinking, but my concern is that they may be buried more deeply than he remembers. Which of the following would be your first choice? 1) TDI/SPP with 12 in round mono and 16 V battery pack. 2) X-Terra 705 w/15 in Coiltek 3kHz. 3) Gold Bug Pro (19 kHz) w/15 in Nel Attack. 4) F75 black (13 kHz) w/11x7 in^2 coil operating in cache process. Assuming he has the time and patience I'm going to have all four with me to do a comparison, but I'd like to start with the one that gives me the best chance. Your advice is appreciated.
  • Create New...