Minelab Electronics Eureda Ace Dual Frequency Detector
By Andy Sabisch
From Page 24
May, 1992 issue of Lost Treasure

Minelab Electronics, the Australian-based metal detector manufacturer, has developed the reputation of building high quality detectors that work well under a wide range of conditions. The Eureka Ace incorporates several unique features in its design, and I was looking forward to testing this new unit in the field when I heard it was being sent to me.


The Eureka Ace is a manual ground-balance detector which operates in the all-metal mode and was designed to be used primarily for electronic prospecting.

The detector is mounted on a modified S-shape rod and, at just over 3-1/2 pounds, is both lightweight and well balanced. The control housing features a built-in bracket which snaps securely onto the shaft and can be mounted in one of three positions to allow the user to adjust for individual hand and finger sizes. The armrest, which doubles as a detector stand, is also adjustable thereby allowing users to compensate for different arm lengths.

The detector comes with an extension cable and a water-resistant nylon bag to allow the control housing to be hip-mounted. This feature is extremely convenient when searching for extended periods of time, particularly with the optional 12-inch elliptical coil, or in shallow creeks and streams where nuggets might be found.

The controls on the Eureka Ace are three knobsSensitivity, Threshold, and Ground Balance; and three toggle switchesOn/ Off, Frequency Select, and Gain Select. The SENSITIVITY knob, located below the speaker on the face of the control housing, is used to adjust the strength of the signal being transmitted from the coil and should be adjusted in conjunction with the GAIN SELECT toggle switch which is discussed below.

The THRESHOLD control is used to set the audio level heard through either the internal speaker or a set of headphones. The GROUND BALANCE knob is a 10-turn control which allows the user to accurately compensate for any ground mineralization present in the area to be searched.

The GAIN SELECT toggle switch, located in the center of the face plate, is a three-position switch labeled BOOST/DIFFI-CULT/NORMAL and is used in conjunction with the SENSI-TIVITY knob. The SENSITIVITY control should be set as high as possible without overloading the Eureka Ace. If excessive chattering or falsing occurs, use the GAIN SELECT toggle switch to eliminate it.

The NORMAL setting should be used in most areas, and if the mineralization encountered is excessive, the signal gain can be reduced by selecting the DIFFICULT mode. In areas where the mineralization is quite low, such as beaches or some dry placers in the southwest, the BOOST mode will amplify the signal and provide a noticeable increase in detection depth.

The most unique feature of the Eureka Ace is the FREQUENCY SELECT toggle switch located just above the GAIN SELECT switch. This control actually allows the user to select one of two different operating frequencies simply by moving a toggle switch. The 8 KHZ frequency allows the detector to penetrate deeper; however, it is not quite as sensitive to small targets such as rice-sized nuggets as the 19 KHZ frequency is. This actually provides two distinctly different detectors in one housing and changing from one to the other is as simple as flipping a toggle switch.

In addition to the two operating frequencies, the Eureka Ace also comes standard with two searchcoils. The six-inch round coil is ideal for searching between rocks and crevices and, combined with the higher 19 KHZ setting, is extremely sensitive to the smaller targets. The eight-inch round coil provides better ground coverage and, when operating in the 8 KHZ mode, results in greater depth on larger targets. Both of the searchcoils feature double-D construction and are sensitive across the entire coil surface.

A headphone jack is located in the lower right corner of the front face plate and accepts the lightweight headphones that come with the detector or any other standard 1/4-inch plug. Since many of the nuggets being recovered .in the gold fields are quite small, a quality set of headphones is recommended to ensure these targets are not in-advertently overlooked.

The Eureka Ace is powered by eight penlight batteries which are contained in a compartment on the bottom of the control housing. The compartment is separated from the electronics to prevent dam-aging the detector in the event the batteries leak.

Alkaline batteries provide approximately 60 hours of use and when the batteries require replacement, a short tone will be heard through the speaker or headphones every 20 seconds.

The factory states that ni-cad rechargeable and carbon batteries should not be used in the detector and, with a 60-hour battery life, they are not really needed.


After unpacking and assembling the Eureka Ace, I proceeded to perform a bench test to see what type of response it produced on various targets one might encounter in the field. I selected the NORMAL setting on the GAIN SELECT toggle switch, increased the SENSITIVITY control to the 3 oclock position, and set the THRESHOLD control so that a faint audio signal was heard through the speaker.

Using the 6-inch coil and selecting the 19 KHZ frequency, I found that the Eureka Ace produced a clear response to the test targets including a 1 pennyweight nugget, a 14 KT gold earring back, and a thin gold chain at fairly impressive depths. By switching the GAIN SELECT to BOOST, an increase of nearly one inch was obtained on the test items. The 8-inch coil produced a negligible difference in detection depth; however, when the 8 (HZ frequency was selected, the increase on larger targets such as a 1/2 ounce nugget and a gold wedding band was dramatic.

I took the Eureka Ace outside to see how the ground balance circuitry handled the mineralized red clay common to north Georgia. Increasing the THRESHOLD control slightly produced an audio signal that would make discerning changes caused by the ground conditions easier to detect. Ground balancing is accomplished by holding the coil about 12 inches above the ground and then slowly lowering it to the ground while listening to the threshold signal.

If the signal decreases, turn the GROUND BALANCE control clockwise to compensate for the mineralization present. This process should be repeated until there is no change in the threshold as the coil is lowered to the ground. All of the items in the test garden were detected by the Eureka Ace, and as observed in the air test, with the combination of the 8-inch coil and the lower frequency, the coil could be raised a few inches above the ground while still detecting the targets.


The first area I took the Eureka Ace to was a small creek south of Dahionega, Georgia, that has produced a considerable amount of gold over the years. Setting the SENSITIVITY control to 2 oclock, the GAIN SELECT to NORMAL, the FREQUENCY SELECT to 19 KHZ, and connecting the 6-inch coil, I quickly ground balanced the detector.

I started out searching a jagged section of exposed bedrock located on the inside bend of the creek, hoping to find a small nugget or two that may have become lodged there during periods of high water. After carefully scanning most of the crevices, I had not received even one signal and began to wonder if someone had been there before me. Just before giving up and finding another area, I received a faint signal that I almost passed up.

Switching to the BOOST mode I rechecked the area and this time the signal was quite distinct. Using a rock hammer and chisel, I began to expand the crack where the detector had indicated the target was located. Removing the debris that filled that crack, I found a shattered .22 caliber bullet wedged in the bottom nearly 7 inches deepunfortunately it wasnt a gold nugget but the sensitivity of the Eureka Ace was readily apparent.

Deciding to try searching some of the shallow pools along the edge of the stream, I quickly removed the control housing and converted it to the hip-mount configuration. The first few signals produced a double-blip when the coil was swept over the target in one direction which is usually characteristic of small ferrous objects. Carefully recovering each of them verified this and by listening to the signal produced by the Eureka Ace, I was able to ignore most trash items such as nails and pieces of wire.

Over the next two hours, I found a number of spent bullets, shell casings, a few pieces of unidentifiable metal, and a 1956 wheat penny at depths ranging from 2 to 8 inches. The changing mineralization and cold stream water had no effect on the operation of

the Eureka Ace which experienced virtually no drift the entire time and required only one adjustment due to some black sand that had built up in one of the pools.

The next area I went to was another creek nearby that still contained a fair amount of gold; however, nearly all of it was extremely fine. While a metal detector would not be useful in detecting the actual gold itself, I was hoping that the Eureka Ace would be able to pinpoint some areas where panning and dredging might be productive.

The first thing I did was sample several areas with a gold pan to determine how much black sand was in the general area and to ensure I would not be tuning the detector over a spot where it was concentrated. After sampling, I proceeded to ground balance the Eureka Ace. Before I began searching, I increased the THRESHOLD control above where I would normally hunt which would allow me to hear any change in the audio level caused by ground mineralization.

Using painted wooden dowel rods, I proceeded to mark areas that caused the threshold level to decrease noticeably. This response was caused by a concentration of black sand or other mineralized material which often held the fine gold flakes. After marking several promising areas, I put the detector down and started sampling each spot with the gold pan. All of the areas held a fair amount of black sand and fine gold and one spot, just downstream of a large rock, held more gold in the sample pan than I have seen come from any other spot on this creek before. While I did not bring my dredge back to this spot, I will in the near future and hope to do quite well.

With the Eureka Ace I was able to cover almost 100 yards of the creek in less than 2 hours and locate several good areas that deserved further investigation. In areas where very little coarse gold exists, this technique will greatly improve your odds for locating pay streaks in the streams you are searching.

Having tested the Eurekas prospecting capabilities I decided to see how well it would work for relic hunting. Realizing that the lack of discrimination would be a drawback in some sites that were littered with nails and pieces of barbed wire, I chose a well-preserved Civil War trench-line that was located just across the Chattahooche River from the city of Atlanta to test the Eureka Ace.

Since the area had been hunted by literally hundreds of people over the years, I realized that most of the targets would be deep so I put on the 8-inch searchcoil and selected the 8 KHZ operating frequency. There were high-tension towers in the immediate area, and with the sensitivity in the 2 oclock position I received some interference and falsing from them. By switching to the DIFFICULT setting, the interference was eliminated and I was hoping that other hunters had also been plagued by this interference and missed some artifacts.

After several minutes of searching the bottom of the trench, I received a faint but distinct signal. By switching back to NORMAL in order to recheck the signal, I was able to determine that it was indeed worth recovering and not caused by a hot rock. Digging was quite difficult due to the tree roots that lined the trench; however, after removing over 9 inches of red clay, I saw the tell-tale white patina of a .58 caliber Civil War round musket ball. Passing the coil over the empty hole produced another faint signal. Removing an additional two inches of dirt, I found another unfired musket ball in perfect conditionthe prospects for this site were looking up.

The next signal produced the characteristic double-blip that I described earlier, and the target turned out to be an old square nail at just under5 inches. After listening to the signal produced by several of these nails I found that I could easily ignore them and increase the number of good targets being recovered. I spent nearly three hours searching most of the visible trench-line and recovered 18 Civil War bullets of various calibers and a Confederate enlisted mans jacket button. By using the audio-discrimination technique, I had only dug one large rusted bolt, and the square nails mentioned previously.

Before leaving, I switched to the 19KHZ frequency and re-searched a small area near one end of the trench. Almost immediately I received a faint signal which disappeared when I switched back to the 8 KHZ frequency. Carefully removing the layer of leaves and a few inches of dirt, I rechecked the hole. The target was in the loose dirt so I picked up a handful and passed it in front of the coil.

When the Eureka Ace responded, indicating that the target was in my hand, I slowly emptied it and found a fired percussion cap which is smaller than the size of a .22 caliber short casing. Despite carefully searching the immediate area I failed to locate any other artifacts and began the long walk back to the truck.


While the Eureka Ace has been designed with the electronic prospector in mind, it has both the features and sensitivity to perform well in beach hunting and relic hunting applications. Despite the lack of discrimination, small ferrous items can be ignored based on the type of signal they produce and this difference can be quickly picked up after only a few hours of practicing in the field.

Some prospectors have found that by snapping the control housing under the armrest the balance is improved and it is less tiring to use in the rod-mounted configuration for extended periods of time. If you dont like using a detector in the hip-mount configuration, you may want to try this technique.

Since the Eureka Ace is actually two distinctly different metal detectors in one housing and includes two coils designed to handle almost all situations, it is an exceptional value for the price of the unit. By initially searching an area with the 6-inch coil in the 19 KHZ mode, and then again with the 8-inch coil in the 8 KHZ mode, users can be certain that very little will be left for the next treasure hunter.

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