Tesoro Electronics Piranha
By Andy Sabisch
From Page 16
December, 1996 issue of Lost Treasure

Since its beginning in 1981, Tesoro Electronics has developed the reputation of providing state-of-the-art metal detectors at affordable prices. Owner and founder Jack Gifford, an avid treasure hunter himself, has always kept this goal at the forefront of his companys research and development efforts.

One of the most popular forms of treasure hunting today is searching for coins, jewelry and other artifacts along the beach and in the shallow water just offshore. Tesoro ventured into the water hunting market with the introduction of the Stingray in 1991. Receiving rave reviews from treasure hunters worldwide, Jack and his staff began developing a pulse-type detector for maximum performance in areas with adverse ground conditions. Following several years of research and testing, the PIranha was born.

The first thing you will notice that is unique about the PIranha is the spelling. The capitalized PI stands for Pulse Induction.


The basic theory behind pulse detectors is not new, having been developed more than 20 years ago to let metal detectors locate deeply buried targets in areas containing highly mineralized soil or a mixture of salt water and black sand. These conditions greatly limit the detection depth one can achieve on a TR- or VLF-type detector, even on some of the more advanced units with computer-controlled ground balance circuitry. But Tesoros engineers did not just repackage an old circuit. Refining the pulse circuit to fit their specifications, the PIranha has a number of unique features.

As with Tesoros other waterproof detector, the Stingray II, the PIranha uses the time-proven housing which has been designed to remain leak proof at depths of as much as 200 feet. Two metal clamps and an O-ring help ensure that water will not get inside and damage the electronics. A positive feature shared with the Stingray II is the ability to use different sized search coils. No longer does a buyer have to decide which size coil they want at the time of purchase. With both a 7- and 101/2-inch coil available in addition to the standard 8-inch version, treasure hunters can select the coil that will give them optimal performance under any condition. All three coils use the Printed Spiral design which is another first for Tesoro.

Rather than using turns of copper wire as found in other detector coils, the PIranha coils are actually a circular printed circuit board encased in epoxy resin. This reduces false signals caused by bumping the coil against a hard object such as a rock, increases sensitivity to smaller targets with windings across the entire coil face and results in less drift from changes in coil temperature.

The PIranha is probably the easiest detector to actually tune in the field requiring only a single adjustment before you start hunting. The lone knob on the face of the control housing turns the unit on, activates the automatic battery check feature and sets the audio threshold heard through the comfortable, waterproof stereo headphones. The only other adjustment on the detector is an internal volume control, to increase the volume to hear over the air bubbles coming from your regulator when scuba diving.

The one aspect of a pulse detector that sets it apart from others is that it will respond to all types of metal pulse units do not have discrimination circuits such as those found on detectors used for coin hunting. While some readers may begin to question why anyone would want a detector with no discrimination, keep in mind what its intended use is. When searching saltwater beaches, shipwreck, or even mineralized areas in the gold fields, you are looking for deeply buried targets that others have missed. The increased detection depth and improved performance provided by the PIranha more than offsets its lack of discrimination.

Powered by eight AA batteries, you should be able to get at least 20 hours of operation on a set of alkaline batteries. Nicads can also be used.


Since the PIranha is a water detector, I headed to the South Carolina coast for my initial test. I headed to the resort beach on Kiawah Island. It would be a good test of the unit since this particular beach contains a great deal of black sand, which greatly limits the depth at which most detectors can locate targets. As anyone who has hunted ocean beaches knows, unless sand has been stripped off the beach, even recently lost coins tend to be quite deep.

The tuning procedure couldnt be easier. I simply turned the unit on, waited for the automatic battery check to finish, and then set the threshold for a faint background hum. Lowering the coil to the damp sand near the waterline, I began searching. The capabilities of the PIranha quickly became apparent as I began to find coins at depths of as much as 12 inches in the wet sand. Neither the saltwater nor the black sand affected the threshold signal. As I wandered up and down the beach I did not have to make a single adjustment of the Threshold control.

After an hour or so I began to determine that iron objects such as nails, hair pins and Fourth-of-July sparkler sticks produce a different signal than coins, keys and other non-ferrous targets. The signal from the junk items was not consistent as the coil was swept across the target from different directions. A double-blip or washed-out response was generally trash. With a little practice, I learned that I could ignore many of these unwanted targets. While not as accurate as a target-ID discriminator, I found it easier to pass up some of the ferrous targets one usually finds with the PIranha than with some of the other pulse units I have tried over the years.

I spent 15 hours hunting several of the public and resort beaches around Charleston during the next few days and in each case found the PIranha to handle the severe black sand conditions with ease. As a testimonial to its sensitivity, I recovered a small (2 dwt.) 14-carat pinky ring on Isle of Palms at a depth of 6 inches in the wet sand. As we prepared to head back home, I looked over my finds. In addition to a pile of corroded clad coins, I had found three gold rings, several pieces of costume jewelry, a Civil War minnie ball and the usual assortment of keys, toy cars and cigarette lighters all in all a successful trip.

Even though the PIranha is designed primarily for use in or near the water, I decided to see how well it performed at some nearby land sites with adverse ground conditions when I arrived home. The first site I went to was Brush Mountain, the site of some Civil War activity before the Battle of Atlanta. The ground is not only extremely mineralized, but it also changes every few feet, which has rendered almost every detector used there useless.

Opting for the 101/2-inch coil for maximum detection depth, I hiked up the mountain to a wooded area overlooking the valley below. As when I hunted the saltwater beaches of Charleston, tuning was quick and easy. Setting the audio threshold for a slight hum, I started across the face of the mountain. The first signal came a few minutes into my hunt. Pinpointing the target, I moved a rock aside and began digging. At a depth of seven inches, I saw the telltale white oxidation of a minnie ball buried since the 1860s. Tucking it into my pouch, I continued on with my hunt. The next few signals turned out to be rusted sections of barbed wire which had been strung in the area since the Civil War.

Again, with a little practice, I began to learn the difference in what a long, ferrous target sounded like as compared to a non-ferrous target such as a bullet or shotgun shell casing. The next good, consistent signal came from the base of an old rotten tree. After several minutes of struggling through the roots and rocks, I added another period bullet to my collection. Midway through my hunt, I switched to the smaller 7-inch coil and began searching among the rock piles that dotted the face of the mountain.

Targets were quite numerous with several of them dating back to the Civil War. After two hours I headed back to the truck and emptied out my pouch. While I did have a small pile of unidentifiable rusted trash, I had also recovered four bullets, a crushed Union button and several percussion caps, which are about the size of a .22 caliber shell, which the 7-inch coil had pulled out of the rocky areas. As I drove home I began to think I had found the secret of how to successfully hunt these sites.


Looking at the detectors currently on the market, its sometimes hard to imagine how any of us that were hunting 20 to 30 years ago actually found anything. The PIranha is a perfect example. With its printed circuit searchcoil, extreme detection depth and rock-stable operation under virtually any condition, the PIranha is light years ahead of what was available even a few years ago. The engineers at Tesoro have definitely done their homework many of the PIranhas features such as interchangeable search coils, long battery life and a durable, water-proof case were incorporated based on feedback received from long-time treasure hunters.

The PIranha sells for $599 and comes with Tesoros limited lifetime warranty a first in the industry as far as water detectors go. That fact in itself says something as far as how strongly Jack and his staff are in their belief that the unit can withstand the rigors beach and water hunting can put on a detector.

Call (800) 528-3352 or write Tesoro at 715 White Spar Road, Prescott, Ariz. 86303 for more information on the PIranha or to obtain a copy of Tesoros informative metal detector information booklet. Be sure to mention you read about the new PIranha in Lost Treasure.

Copyright © 1996-2018 LostTreasure®, Inc. All Rights Reserved.