White's Goldmaster 24K With 4"x6" DD Search Coil

[Steve Herschbach]

On 3/27/2022 at 11:52 AM, Mitchwaller said:

Hi Steve,

Thank you for ALL of your work and what you do, you are greatly appreciated!

I've been running the Garrett's 24K with the 6X10 and the 6" concentric coils with no issues, but when I put my 4X6 GMX coil on and run the sensitivity above 7, I get the extreme overload noise and display. Shouldn't I be able to run it up to level 10 on sensitivity like the others? I'm wondering if I've got a defective coil...

Then they are defective. Though they can be used still, as long as gain not run too high. Sorry to hear that, and not sure what can be done about it at this point. Contact the service center pinned at top of forum, fingers crossed.

Coils were always an issue with White’s. If you ever got a new detector from them DOA, chances are it was overloading from a bad coil. Never could figure out how they got out of the factory like that. Coils may have been very borderline, tested ok, but further curing of epoxy later put them out of tune? Don’t know, just speculating.

[Geotech]

19 hours ago, Steve Herschbach said:

Coils may have been very borderline, tested ok, but further curing of epoxy later put them out of tune? Don’t know, just speculating.

Yes, long-term epoxy shifts were the cause. The 4x6 was especially problematic because the whole thing was embedded in a single epoxy pour. We were baking coils for a week and then letting them age for 3 months, and every coil was re-tested before shipment. Yet there were still returns.

Fortunately the 4x6 is not hard to open and very easy to re-null.

[kac]

Is there a shrink issue with the epoxy when it reaches full cure?

[Geotech]

Not unless it's sensitive to temperature. The problem was that "full cure" was a lot longer than expected and the 4x6 was especially sensitive to very minute shrinkage. But even the 10" DD used on the V3 was problematic, a lot of coils got replaced early on.