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Date Posted: 10:54:42 03/31/03 Mon
Author: Steve Herschbach
Subject: My Tesoro Pinpointer

The more I work with pulse induction (PI) metal detectors with large coils, the more I wish I had a good pinpointer. It can be hard to pinpoint with the larger coils, especially when the target ends up being a deep, elongated iron or steel object. They tend to throw the signal off to one side or the other. Which raises the secondary issue of poor iron discrimination with PI detectors.

I have tried several pinpointers but so far have not found one that quite does what I want. Most have too limited a detection range, poor sensitivity to gold nuggets, and most lack any kind of discrimination ability.

So I decided to make my own pinpointer. Basically, what I want is a very small metal detector. So I chose the Tesoro Silver uMax as my base unit. I cut the armrest off at the end of the foam grip, in effect giving the unit a pistol grip. I removed the middle rod section and inserted the cut-down plastic isolator rod into the grip section. The isolator was cut down as far as I could go and still allow enough room to wrap excess coil cable. This ended up making the isolator 7" long.

The stock 7" coil is too big, but Tesoro has a nice little 4" coil for the uMax. This was attached to the isolator with a Fisher nylon wingnut instead of the steel screw Tesoro uses. I had to drill the hole in the isolator out slightly for the nylon wingnut. The overall unit is 15" long. All I have to do now is put a little hook on it to hang it on my belt.



The unit is very sensitive, easily getting a signal on a 2 grain gold nugget. It will hit a 4 grain matchhead-size nugget at about 2". It hits small nuggets better than I really expected. It hits a silver dime easily at 5". Better yet, it has good iron and steel discrimination.

This means I will be able to use the unit to verify the identity of some targets. Even deep iron items that are way beyond the range of this little detector initially may be identified as the hole is excavated. I've really done battle with some targets in difficult to dig soils, particularly when tree roots are involved. Anyone that has spent 15 minutes to get an old can knows what I am talking about. Not only will this unit help me find out if the target is actually just off one side of the hole, but it will reveal that some items are iron as I close in on them. It will also help finding some marginal nuggets in a pile of soil. Sometimes you get them out of the hole and they just disappear. This will be of great aid when I nugget hunt with my Minelab GP Extreme outfitted with an 18" or larger coil.

I am also starting to explore using my Garrett Infinium for coin detecting. One problem is that PI detectors are very fond of steel wire. Hairpins, tiny nails, paper clips, and other small steel items give a good signal, but luckily at shallow depths. This unit should help eliminate many of these questionable small surface targets. It has a simple switch between all-metal and disc modes, so if the target is accessible in all-metal but drops out at the chosen disc level it can be ignored. If it does not signal in all-metal it is a deeper target.

If Tesoro actually built this unit for resale it would probably sell for under $200 street price. But since I had to buy a whole machine and discard unneeded parts plus add the 4" coil the cost to assemble this is about $310 street price. The good news is that with a spare armrest I have a pinpointer that can be converted back into a very capable little metal detector. The Silver umax is a great backup detector. The Silver uMax suggested retail is $299.00 - for more info see http://www.tesoro.com/SilverMicroMaxDataSheet.htm The 4" coil has a suggested retail of $89.00.

Of course, this is all just theory at the moment. Maybe I will find the unit too bulky for practical field use. It will mainly just depend on how well it really works in practice. This little unit packs a lot of punch so it may prove worth its place on my belt. I'll keep you all informed.

Steve Herschbach
Steve's Mining Journal

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