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Tesoro Mayan built from 11/82 thru 6/88.

August 12, 2013 05:50AM avatar
I just picked up a old Tesoro Mayan on eBay. When I received it I was very pleasantly surprised that it looks brand new. No scratches at all on the housing, no wear marks on the stem and o scratches on the coil bottom. The inside of the housing and circuit board are just as clean as the exterior. The detector was shipped in its original box which is also in great shape. It seem like it was bought and maybe used in someones yard and then put away in the closet and forgot about.
The last Mayan and Inca (the Inca being in the same housing/rod design except a VLF/VLF-Disc. model) were both in "as new" condition. They didn't come in their original factory box but looked as if they could have.

The original search coils was the 7" on the Mayan and 8" on the Inca so I presume yours had the7"? That was my all-around favorite search coil on virtually all Tesoro Discriminators.

The Mayan is an old VLF / TR from the early 80's that operates at 12 kHz.
Correct, with the build dates at Tesoro in the subject box. It is interesting to note that many terms we used back then, from '75 thru the '80s, have been lost in translation or not understood due to terminology used with our more modern metal detectors. I mean you figure the last build date of the Mayan was over a quarter-of-a-century ago! So many newcomers to the hobby really don't know what is meant by lingo like VLF or TR. If you don't mind, let me clarify it for readers who are new to the sport.

First, the more correct title for the Mayan is a VLF/TR-Disc. operation detector.

'TR', or more correctly 'T/R', stands for the Transmit/Receive principle of operation. A popular term of operation seen in the late '60s and early '70s was 'I/B' (Induction/Balance) which is basically the same description of function. In time, the 'T/R' reference became more popular and was normally used. Most people would select between a 'BFO', Beat Frequency Oscillation or 'T/R' method of operation.

'T/R' detectors operated from about 50 kHz to 100 kHz, with the vast majority within a very small variance of 100 kHz.

In the early 1970's Discrimination was added to some of the conventional TR operating models to create a 'TR-Disc.' model, allowing an ability to vary a level of Discrimination to ignore unwanted trash, such as iron, foil and pull tabs. TR-Disc. units became very popular for Coin Hunters.

'VLF', brief for Very Low Frequency,is a term that most manufacturers used to describe modes that use the 'T/R' principle of operation, but they are designed to operate in the VLF range between 1 kHz and 30 kHz, with the majority being from 6.59 kHz to 15 kHz ad a few models slightly lower or higher. So, a 'VLF' detector is still a 'TR' detector, except at a much lower operating frequency.

The reason to make the, work in that general frequency rage is it gave the design engineers the ability to incorporate circuitry that would let the user cancel out the effects of the ground mineralization. Traditional or conventional TR and TR-Disc. models need to have the Threshold tuning adjusted with the search coil held a certain distance from the ground mineral, and then the search coil sweep maintaining that same coil-to-ground relationship.

If the coil is lowered toward the mineralized ground it will null out or go silent due to the stronger ground mineral reading, and if the search coil is lifted away from he ground, such as to go over a pine cone or dandelion, the audio would get much louder because the ground mineral influence was moved farther away from he search coil.

So, when we used the term 'VLF' we were describing both the operating frequency range AND describing the tuning function of cancelling out the ground mineral signal. When the ground mineral is canceled or rejected or discriminated, the end result is that the metal detector was then going to respond to any metal, ferrous or non-ferrous. We referred then to a 'VLF' operation as an 'All Metal' mode.

Manufacturers started out using the 'VLF' term to describe their ground-cancelling All Metal modes, but soon they changed to use other terminology to describe this function or search mode, such as:

GA (Ground Adjust)
GB (Ground Balance)
GC (Ground Cancel)
GEB (Ground Exclusion Balance),
GNC (Ground Neutralizing Circuitry)
Normal and
All Metal

Avid Relic Hunters, especially, loved the VLF or Ground Balanced All Metal search mode because they were looking for everything, ferrous and non-ferrous, and appreciated being able to cancel out the ground mineral for ease of operation and even added depth due to the much lower operating frequency range.

Most Coin Hunters, however, didn't like the new 'VLF' models because they didn't want to have to hear signals on all of the nails and wire and bolts and bobby pins and gum wrapper foil and bigger foil and even pull tabs. They preferred to reject the common trash from detection (from signaling), so manufacturers came up with the dual-mode operation metal detectors, the 'VLF/ TR-Disc.'

The 'VLF/TR-Disc.' models allowed the operator to search in the VLF or All Metal ground-balanced mode for ease-of-operation to locate ANY target in an area, then switch to the old conventional TR-Disc. mode to help Discriminate the junk and only hear the higher-conduct targets, such as coins and good jewelry, etc. The downfall is that operating in the TR-Disc. mode that operated in the VLF range, the detectors were a little more reactive to variance in the coil-to-ground relationship. They also didn't get as good a depth as the Ground Balanced VLF mode.

In 1978 we got our first detector model which cancelled the ground mineral (operated in the VLF range) AND Discriminated unwanted targets. Thus it ignored the ground signal and Discriminated, and that meant it was working in a 'VLF-Disc.' mode. To accomplish this the search coil had to be swept at a brisk sweep speed to feed in and process out the ground signal and pass along the detected target signal. We then also got the new term 'Motion Discrimination' to refer to the VLF-Disc. mode of operation.

The first such models required a very fast sweep speed and most Coin Hunters didn't like hat and preferred the earlier TR-Disc. mode to reject trash as no motion was required. So, manufacturers then produced the VLF/VLF-Disc./TR-Disc. detectors that had 3-modes of operation (described as the Ground Balance All Metal mode / Ground Balanced motion-Discriminate mode / conventional TR-Discriminate mode).

I've played around with it on my patio and it picked up my gold wedding band which was under two big rusty nails. As the coil passed over the nails the threshold nulled and then the ring rang out nice and smooth on the ring. Hopefully I can use the TR mode at the old library in town which is full of iron targets and pick out some older silver coins and nickles.
That was a strength of most 'conventional' TR and TR-Disc. models, the ability to just ignore many iron nails and respond to a coin in the mix, such as one or two nails on/by a coin.

I know with a TR I need to keep the coil an even height above the soil to keep it from falsing. Its been over 15 years since I've use a TR detector and that one was a Garrett Scorpion. From what I can remember about the TR operating mode of the Garrett it seem the Mayan is lot more stable and easier to use.
Correct, you must retain a uniform coil-to-ground relationship.

Now I'll be able to try reverse discrimination. If I remember correctly you search in all-metal VLF mode, acquire a target, then pin point the target and place your coil on top of it. Then switch to the TR mode and slowly move the coil away. If the threshold sound decreases the target was above your TR mode discrimination setting and if the threshold sound increases the target was lower than the discrimination setting. The Mayan makes this easy since the push button on the handle changes the mode from VLF to TR and vice-versa.
'Reverse Discrimination' is a term rarely heard today, because TR-Disc. is also rarely used today, or even incorporated in a model. Think of it simply as a Reverse Response method to check a located target in the TR-Disc. mode.

Because the VLF/TR-Disc. models were more touchy in the TR-Disc. mode due to the much lower operating frequency, on method some Coin Hunters used to maintain the uniform coil-to-ground relationships was to simply place the search coil on the ground and keep it that way during a search, or when isolating a target to check in the TR-Disc. mode. That also created a new term called 'scrubbing' where the coil was 'scrubbed on the ground.'

Due to the uneven texture of the ground, sometimes dirt of simply the grass between the coil and ground, it was a little more difficult to check a located target. In a normal search you would use the VLF All Metal mode, search for any target, pinpoint it, then position the search coil just off to the side of the target and close to the ground.

Toggle or switch to the conventional TR-Disc. mode and move the search coil over the located target. You would listen for an INCREASE in audio from a desired object, such as a coin that was more conductive than the Discriminate setting. If you use Reverse Discrimination you are listening for a Reverse Response to alert you to a potentially good or bad target. Thus, if you move the coil off of a conductive target you would hear a DECREASE from a potentially good target.

Naturally, the reverse is true and you'd hear an INCREASE if you moved the search coil away from a rejected target, such as an iron nail.

If anyone ((Monte?) has any tips on operating the Mayan I would sure appreciate them.
Sorry to ramble ion for new readers to metal detecting technique, even though this is old-technology and not used today for many reasons.

Most detectors made today, and really most made in the past decade or so, do NOT have a 'conventional' TR-Disc. mode.

TR-Disc. could use that method, although not always successful or easily achieved, because it wasn't relying on the Ground Compensated mode.

VLF (All Metal) and VLF-Disc.(Ground Balanced Discrimination) search modes ARE dealing more with the influence of the ground mineral on the EMF (electromagnetic field) and it is important to keep the search coil a good 1" to 2" off-the-ground when searching. If the coil is worked too close to the ground, it can experience overload and/or falsing and/or loss-of-depth, depending upon the severity of the ground mineral

Also remember this. The more modern motion Disc. operation will often provide depth-of-detection close to that of the standard All Metal mode, and with some makes and models it might even be a little better or deeper.

The conventional TR-Disc. mode, however, will seldom come close to the depth achieve by the VLF All Metal mode so checking targets the operator needs to be alert to this condition. That is, if checking a pinpointed target in the normal fashion by starting with the coil to the side of the target, and making sure there is a slight Threshold-hum in TR-Disc., a positive increase would suggest a desired target above the Disc. setting, a nulling of the Threshold would indicate the target was rejected, and NO SIGNAL CHANGE would suggest that the target might be accepted or rejected, but is deeper than the TR-Disc. mode can respond to. Therefore, it needs to be recovered.


"Your EYES ... the only 100% accurate form of Discrimination!"

Stinkwater Wells Trading Post
Metal Detector Evaluations and Product Reviews
I'm now 'back home' in Farr West Utah
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Subject Author Views Posted

Tesoro Mayan

ArizFlash 1462 August 09, 2013 06:35PM

Tesoro Mayan built from 11/82 thru 6/88.

Monte 3124 August 12, 2013 05:50AM

Re: Tesoro Mayan built from 11/82 thru 6/88.

ArizFlash 1197 August 12, 2013 02:49PM

Back to you ....

Monte 1061 August 13, 2013 09:06AM

Re: Tesoro Mayan built from 11/82 thru 6/88.

WM6 885 August 12, 2013 12:28PM

Re: Tesoro Mayan built from 11/82 thru 6/88.

ArizFlash 970 August 12, 2013 02:07PM

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