Fisher M66 Valve & Box Locator
Fisher M66 Valve & Box Locator
Fisher M66 Valve & Box Locator
Fisher: Since 1931

Fisher M66 Valve & Box Locator

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Customer Reviews

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Derek Carmichael
M66 locatlor

I’ve been using the M66 metal detector for the past 2 years in the natural gas utility industry and it hasn’t ever let me down. If there was something the could be found I found it even buried 8” down. I don’t often play with the sensitivity, only when I can’t find our facilities right away and they are buried a couple inches down. All around a great locator.

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Product Description

The Fisher M-66 is an all-metal, professional-grade metal detector designed specifically for utility workers, municipal crews, and contractors. Engineered for simplicity and effectiveness, it excels at locating valve boxes, manhole covers, and other buried metallic infrastructure—even through asphalt and concrete. A standout feature is its double-D search loop, offering stable performance and deeper detection.


Operating at 4.5 kHz, the M-66 provides consistent and accurate detection of ferrous and non-ferrous metals. Its analog meter and audio tone alert users to changes in signal strength, ensuring quick identification of buried targets. The detector uses manual tuning and ground balancing to adapt to varying soil mineralization, while the threshold-based Tuning Control allows users to optimize sensitivity. The search loop is immersible, supporting work in wet environments.


Built for demanding field conditions, the M-66 features a rugged frame with an adjustable shaft (28"–48") and an 8" waterproof coil. Weighing just 4.25 lbs, it offers comfortable handling over long shifts. Powered by dual 9V batteries, it delivers extended operation and includes a battery test function to prevent downtime. The control layout is intuitive, making it easy to train new users and ensure reliable performance in daily operations.


Purpose: Valve & Box Locator

Specifications

Manufacturer: First Texas Products, LLC
Brand Name: Fisher Research Labs
Country of Origin: USA
Warranty: 2 Years
Output Frequency: 4.5 kHz
Audio Output: 450 Hz via 16-ohm speaker
Power Supply: 2 x 9V batteries
Power Consumption: (-9V) 17 mA; (+9V) 4 mA min, 6 mA sound threshold, 125 mA max sound
Weight (with 8” coil): 4.25 lbs (1.93 kg)
Operating Temperature: -4°F to 158°F (-20°C to 70°C)
Search Coil: 8" fully submersible
Adjustable Shaft Length: 28" to 48" (71 cm to 122 cm)
Shipping Weight: 7 lbs (3.18 kg)
Shipping Dimensions: 34.75" x 12.75" x 5.25" (88.3 cm x 32.4 cm x 13.3 cm)
Target Indication: Analog meter and audio tone
Tuning & Ground Control: Manual threshold and ground rejection controls
Metal Detection Type: Detects all metals including aluminum, brass, copper, iron, nickel, steel, and tin
Design Features: Weather resistant, built-in battery test, simple 2-knob operation

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Manual

M66

Support

For more information and to purchase, visit where to buy , email us , chat with us, or call us at 1-800-685-5050   for any questions.
For repair service in warranty or out of warranty please fill out the RMA form.

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Frequently Asked Questions

How deep can the M-66 detect metallic objects like valve covers or manhole lids?

Detection depth depends on object size, orientation, and ground composition, but typical depths are: valve boxes up to 10", manhole covers up to 24", and large ferrous objects up to several feet. Ground balance and tuning directly impact depth performance.

Can the M-66 distinguish between different types of metal?

No, the M-66 is an all-metal detector and does not provide discrimination. It is designed to detect all metals equally, which is ideal for utility work where both ferrous and non-ferrous targets must be located.

How does the Ground Rejection feature work on the M-66?

Ground Rejection allows manual balancing of the detector to compensate for soil mineralization. Proper tuning eliminates background noise caused by naturally conductive soil, enhancing target accuracy and reducing false signals.

What’s the proper technique for tuning the M-66 in highly mineralized ground?

Begin with the Ground control at “5” and the Tuning control adjusted until a slight threshold tone is audible. Lift the coil 12" off the ground—if tone increases, raise Ground setting; if it decreases, lower it. Repeat until tone remains stable when lifting.

Is the M-66 effective through paved surfaces like asphalt or concrete?

Yes. The M-66 is designed for utility environments and can effectively detect targets buried under paved surfaces. Its low-frequency operation and manual tuning provide excellent penetration and stability.

How does the analog meter assist in locating buried objects?

The analog meter provides a visual representation of field disturbances caused by metal objects. Combined with audio signals, it helps users visually interpret signal strength and pinpoint target boundaries.

Can the M-66 search coil be submerged, and if so, to what extent?

Yes, the 8" coil is fully submersible and can be used in shallow water or wet environments. However, the control housing is not waterproof and should remain dry during operation.

What is the best sweep pattern for locating valve and box covers?

Use a slow, consistent side-to-side sweep, maintaining a uniform coil height. Overlapping each pass ensures complete ground coverage, especially when locating small or deeply buried targets.

What are the common signs of low battery, and how do they affect performance?

A battery check reading below 80 on the analog meter indicates low power. This may result in reduced detection depth, unstable signals, and inconsistent meter readings. Always check batteries before use to ensure optimal performance.

Testimonials

What Our Customers Are Saying

'...he found his first coin. A 1946 wheat. I'm glad to say we have a new Digger in the family."





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Landon Howlett

Fisher F70

This is a Union Officers belt plate from the Civil War, it was found at a G.A.R. 1895 Civil War reunion encampment...





JimDoan

Jim Doan

Bounty Hunter Quickdraw II

'...great detector please keep me informed on the new machines coming out i got pictures of your detectors for years finding things in fields that have been hunted by everything till the First Texas hit the ground.'


RyanVecchio1

Ryan Vecchio

Bounty Hunter Platinum

"Great contact information, wonderful interaction and the product is wonderful. I will expand my accessories, new usable work products, thanks for this convince and an all USA (EL Paso TX) buy local products."
JamesKSample

James K. Sample

Fisher TW6

'...i pulled the trigger on it just in time to detect the new yard my son was on and all i can say is this machine is one serious coin shooter the first yard I scan with it I get my first silver quarter (1946) and my first Morgan dollar (1900) which was 11in .

DaveBrumfield

David Brumfield

Bounty Hunter QuickDraw Pro

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