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Sven, about the GB & Disc. adjustments with a Sidewinder µMAX.

July 28, 2018 09:22PM avatar
Quote
SvenS
Just read your post about adjusting GB.
From what I read, if GB'ing at min disc setting and moving the disc up, GB goes negative and I would have to adjust GB to be more positive. And if I reduce the disc, I have to adjust back negative.
Your deduction is incorrect ... or I goofed in my post about the Sidewinder µMAX, most original Conquistadors (pre-µMAX branding) and a few other Tesoro models.

The circuitry design glitch is this:

Adjusting the variable Discrimination control will also shift the Ground Balance from the internally trimmer preset setting. Increasing or decreasing the Disc. control from the setting it was at when the GB trimmer was adjusted, will shift the GB the same direction as the change in the Discriminate control.

Example #1: If the Disc. level is set at the absolute minimum of the ED-120 Disc., and then the GB trimmer is adjusted so that the All Metal/Pinpoint GB reference is 'spot on', then you can't reduce the GB setting with the Disc. control, but it will increase the GB setting as the Discriminate control is increased from the minimum setting. Thus, the Ground Balance could end up being way too positive.

Example #2: Let's just say the Disc. level was adjusted to reject small foil and larger foil and was just a bit below the rejection of a US 5¢ 'nickel' coin, and then the GB trimmer was adjusted to be spot on in All Metal/Pinpoint. If the Disc. control is then reduced to the minimum Disc. level, it will also reduce or adjust the GB to the negative. But if the Disc. is increased to reject screw caps, zinc pennies or higher, it will also shift the GB much more positive from the initial trimmer setting.

Note that if the GB is adjusted to negatively, it can cause falsing in the silent-search Discriminate mode. And if it is adjusted too positively, it can eliminate the detection or positive response to higher conductive targets such as large US silver dollars, and even silver or clad half-dollars or more.


Quote
SvenS
Now I do plan on bringing the threshold and GB control to the faceplate so they can be adjusted externally. I will also have a fixed factory GB setting as a reference point.
Such modifications can be very beneficial, such as those done, initially by 'Mr. Bill' Crabtree, to the White's Classic series. The modified Classic ID in my current detector battery is NOT going anywhere. I am at the point in life now where long-time favorites and impressive newcomers are fitted in my arsenal to stay.

However, there are a few important things to consider:

a.. The White's Classic series didn't have a similar circuitry design glitch to deal with.

b.. The modifications were a practical and needed task for the Classic series because the factory made ALL Classic series models as "turn-on-and-go" designs relying on an internally preset GB. Therefore, the consumer had no factory options to consider.

c.. With Tesoro models, you have various models that rely on an internally preset GB trimmer, and most work OK, like the Silver Sabre II or Silver Sabre µMAX (microMAX), while some preset models, such as the Sidewinder µMAX, have a glitch and really need more attention than a modification to move two controls to the outside.

d.. Better still, Tesoro already offers models for those who wish to have external Threshold and Ground Balance controls, such as the Bandido II or Bandido II µMAX and others. To me, it is best just to buy a Tesoro model equipped with the desired features in the first place rather than tinker around with a modification.


Quote
SvenS
On an older Silver Sabre umax---
I have found that replacing the GB trimpot (100K) with an external 3 3/4 turn (100K) multi-turn pot was no better than a single turn. The adjustment range was very small. What I did to increase the usable range was add a resistor to the external control pot to change it into a 50K. It made a big difference.
Models with 10-turn or 3¾-turn GB pots are still touchy with a rather limited range of adjustment in most difficult soils. More of a coarse-tune setting rather than fine-tuning them with a more variable control. I hope your mod works for you.


Quote
SvenS
I will see if changing the value of the original Sidewinder trimpot similar to the Silver Sabre has a similar effect
It might make it less coarse tune, but it won't change the initial circuitry design glitch.

Best of success to you.

Monte

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

Stinkwater Wells Trading Post
Metal Detector Evaluations and Product Reviews
monte@ahrps.org ... or ... monte@stinkwaterwells.com
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Subject Author Views Posted

So I picked up a Sidewinder umax

SvenS 389 July 28, 2018 02:58PM

Sven, about the GB & Disc. adjustments with a Sidewinder µMAX.

Monte 307 July 28, 2018 09:22PM

Re: Sven, about the GB & Disc. adjustments with a Sidewinder µMAX.

SvenS 243 July 29, 2018 07:13AM



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