A coil question for those more technically knowledgeable than me

I've been told with a fixed ground balance detector when you switch coils to one that the detector hasn't been tuned to, you lose performance since the detector isn't going to be precisely tuned to the new coil.

Would the amount of performance loss be tied to how "in spec" the replacement coil is?

Yes.

Although all coils are spec'd to a design intent, there's always tiny variations in manufacturing processes that can introduce some deviation.
While well within design tolerance, this slight difference in impedance can express itself on the detector by being ever so slightly (or occasionally even more than slightly) off from the original coil's impedance...and thus GB setting.

The impedance mismatch can also shift the TID slightly...for the same reason.
That's also why many newer detector designs do an auto impedance match to the coil during power-on / boot-up.



Edited 2 time(s). Last edit at 04/25/2019 07:24AM by Mike in CO.

It's normal for the coil to be manufactured to be within a certain 'specification range' , similarly the control box electronics are made/adjusted to a specific requirement. The end result is that when any two are paired up, they will work as intended.

But obviously there will be small differences, which may be noticed, particularly TID values shift. So it's possible that swapping one coil for another of the same type may give better or worse performance.

Stop worrying about it.

Mike in CO...…… clearly/well-stated.

In addition, your soil may differ from the factory selected set GB.

No worries, Pimento. Just looking to increase my education by getting opinions from those more knowledgeable on the subject than me...like you, Mike and Tom.

I had a Silver Sabre micromax that air-tested on a silver dime at 9". I bought a 5.75 coil from Rusty Henry and had him tune the detector to the smaller coil back before he retired. Wasn't expecting a lot more than 7" but when I got it back I was shocked it was hitting at 9" just like with the bigger coil. That was a fixed GB coil too. Don't know exactly what Rusty did to that unit but I should have never given it up...

marcomo Wrote:
-------------------------------------------------------
> No worries, Pimento. Just looking to increase my e
> ducation by getting opinions from those more knowl
> edgeable on the subject than me...like you, Mike a
> nd Tom.
>
> I had a Silver Sabre micromax that air-tested on a
> silver dime at 9". I bought a 5.75 coil from Rusty
> Henry and had him tune the detector to the smaller
> coil back before he retired. Wasn't expecting a lo
> t more than 7" but when I got it back I was shocke
> d it was hitting at 9" just like with the bigger c
> oil. That was a fixed GB coil too. Don't know exac
> tly what Rusty did to that unit but I should have
> never given it up...


I remember when you told me about that detector/coil Marcus--and that you were going to have Rusty calibrate the Sabre to the 5.75.------We all have detectors coil combos that we wish we would have kept.---At least that's my case also.--------Del

Hi Del, I'll bite my friend. What ones did you regret cutting loose?

When Rusty tuned the 5.75" coil to the detector did the 8" coil still get the same depth or less? I have a Golden uMax that is hot with the 8" Brown donut but most others I tried never came close.
But I recently bought a 5.75" coil and it is almost as hot a the 8 " Coil. The problem with the golden is not so much depth but it will mix tones past 4" or so if coil does not match up well. The 5.75" I bought matches well unlike the precision 7 or 10.5" Concentric I buyed and tried.

marcomo Wrote:
-------------------------------------------------------
> Hi Del, I'll bite my friend. What ones did you reg
> ret cutting loose?


Well, there's been several over the years.---Three that comes right to the front of my mind was the Explorer 2, Bandito 2 micro max (8" & 5.75) & Fors Relic.----I was able to snag another new Relic with stock & 5" coils even though they are now out of production so all is not lost on that one.----The Explorer 2 & Bandito was new & "showroom" when I got rid of them.----What ever induced me to do that I'll never know---but I've been kicking myself ever since.-----Great detectors all three! IMO

Quote Marcomo: "I had a Silver Sabre micromax that air-tested on a silver dime at 9". I bought a 5.75" coil from Rusty Henry and had him tune the detector to the smaller coil. When I got it back .. it was hitting at 9" just like with the bigger coil. I don't know exactly what Rusty did to that unit.".

You really should've provided this information in your opening post, it completely changes the nature of your question.
So .. you're not talking about the same coil, but a different size one (smaller).
And you have no idea what modifications were done to the detector, and are just using the term "tuning" as a catch-all for "modified".
I think it's likely that Mr Rusty has made some significant electronic changes to the detector innards. Probably increasing the electronic gain (amplification) at some point(s) to compensate for the predictable (physics) decrease in signal coming from the smaller coil.
He may also have made adjustments so the detector circuitry better matches the small coil. And, though you didn't say, he may also have modified the coil itself. For example by adding small bits of ferrite / lead on the casing. Are there any signs of coil tampering, like additional plastic pieces bonded onto it?

And the obvious question - did it still work OK or better, with the standard large coil? or was that compromised, by EMI / noise, instability, overload issues etc.?

Good questions all, Pimento, better than my answers. Got rid of the 8" in short order and never retried it on the Silver Sabre after getting it back from Rusty.