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13 Khz F75 Concentric Coils On 19 Khz Series Detectors


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The First Texas 19 kHz series of detectors include the Fisher Gold Bug, Gold Bug Pro, F19, Teknetics G2 and G2+, and the Bounty Hunter Time Ranger Pro.

These detectors are all designed specifically for DD coils. However, a lot of the F70/F75 coils will plug into the 19 kHz models and work, some better, some worse. You can't harm the detector doing this, but the coils may not ground balance properly, or have inaccurate target id. Others may be fine, due to the slop in coil manufacturing tolerances. From this thread we have this commentary by FT engineer Dave Johnson:

1. F75 and F70 searchcoils are interchangeable.

2. T2 coils are their own animal, will not work at all on anything else (or vice versa).

3. F5 uses the "Greek" ("Fratbros") searchcoil series. These are wired the same as the F75/70 searchcoils but are electrically different. Even though some customers have tried searchcoils from one series on a machine designed for the other series and decided that they "work", the factory is not going to say that they "work' because we know there is performance degradation whether or not the customer knows (or even cares) about that.

4. The legacy BH coil series was also used on the Fisher F2 and F4. Although these may plug into F75/70 and Greek/Fratbros machines and actually beep, performance is severely degraded.

5. The 19 kHz machines (Gold Bug and others derived from that platform) are designed specifically to use the DD searchcoils of the Greek/Fratbros series. Depending on the individual searchcoil, a concentric may work fairly well or not at all or anything in between.

6. In general, plugging the wrong searchcoil into a metal detector is not going to cause any damage to the detector although we cannot guarantee a thing like that.

Long story short I have this Time Ranger Pro sitting around that I've basically done nothing with but invest in a NEL accessory coil. Back in the day I ran the 13 kHz Detech Ultimate coil and 4" x 6.5" concentric coils from my F75 on my 19 kHz Gold Bug Pro, and they seemed to work fine. But as noted above it is a crapshoot.

Anyway, I got to wondering about a small concentric on the TRP, and looked into rounding up the 13 kHz 4" x 6.5" concentric for the F70/F75 to give it a go on the 19 kHz TRP. This is where I was reminded that First Texas has redesigned the housing on some older coils, including the old 4" x 6.5" elliptical. The new design replaces the old design, and it is important to note that scuff covers for the old version do not fit the old version, and vice versa.

I ordered one that has a picture of the old design, but frankly I have no idea which of the two coils pictured below will show up. At some point I'll let you all know how this coil runs... or not.... on the TRP.

fisher-f70-f75-concentric-elliptical-search-coil.jpg

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  • Steve Herschbach changed the title to 13 kHz F75 Concentric Coils On 19 kHz Series Detectors
  • Steve Herschbach changed the title to 13 Khz F75 Concentric Coils On 19 Khz Series Detectors

I have kind of the opposite question.  I decided to grab one of the Tek G2+ "Pinky" machines as the price was just too good to pass up for potential relic duty.  My question is whether Detech's Ultimate coil for the F70/F75 is electrically the same as the Ultimate for the F19/Gold Bug/G2/Greek coil?  Note that G2 Ultimate coil is apparently compatible with the 7.8 khz Gamma as well as the 19 khz machines listed. I already have an ultimate for my F75 and really don't feel like shelling out for a duplicate, but also don't want to compromise on optimal performance if those coils actually are different.

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Thanks, Steve.  The fact that it worked for you was encouraging, I just have no way of really benchmarking whether I am getting max performance.  I sort of figure there is some sort of difference because they are separate part #'s (otherwise why not just add F70/75 compatibility to the list?).  Probably splitting hairs if there really is a difference.  Will give it a go nevertheless.  Nothing to lose.

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On 10/4/2020 at 6:53 PM, Steve Herschbach said:

5. The 19 kHz machines (Gold Bug and others derived from that platform) are designed specifically to use the DD searchcoils of the Greek/Fratbros series. Depending on the individual searchcoil, a concentric may work fairly well or not at all or anything in between.  (Dave Johnson)

I bought a used Teknetics Gamma (2nd from top of Frat Bros. line, below the Omega) with stock round concentric and gave it away to a relative.  I later got a good deal on a used 3 coil 'package' (from Ebay) that included the Tek 5"x10" concentric for the Frat Bros. line.  It looked almost identical to the coil shown on the right in the following photo, but had a Teknetics logo sticker in the fat part of the housing (below the attach ears).  I tried it on my Fisher Gold Bug Pro and the first time I turned it on it seemed to work OK.  The second and third time I turned on the GB Pro it squeeled unhappily.  I subsequently sent it to my relative for use on the Tek Gamma.

Coiltek-for-Fisher_and_5x10-conc.thumb.JPG.76f9392a92b66fcc6a40a67130a2d42c.JPG

Some time later I bought the coil on the left in the photo, also used from Ebay.  The seller said it worked on a Fisher F5 and when I asked if it would work on my GB Pro he was cautious and said he didn't know (I believed him).  I took a flyer; I mean who doesn't want to own one of the few Coilteks ever made for a Fisher detector?  😁  I was fortunate and it ran fine.  It became my go-to coil for coin hunting some local parks and I found quite a few (including old) coins with it.  I do recall that it didn't like to Ground Grab consistently as it showed different numbers for the same spot of ground for consecutive grabs.  (And I see Steve say above when referring to putting F75 coils on the Gold Bug "...the coils may not ground balance properly,...")

My third used Ebay buy in this story is the one shown on the right in the above photo.  I bought it from a seller who said it was for the F75 family.  Typically those have a sticker with 'F70' or 'F75' on the fat part of the housing but as you can see, that is missing.  I wanted a concentric for my F75 badly and I took a(nother) chance.  It works, but I was never happy with its performance as it seemed to lack the depth I had read several posters on different forums claim it has.  Depth alone is an unreliable measure since it depends upon other factors, and on top of that I've never gotten a good feeling with concentric coils, so I can't say that I was sold the wrong coil, but I've always wondered.  And now I see this:

On 10/4/2020 at 6:53 PM, Steve Herschbach said:

3. F5 uses the "Greek" ("Fratbros") searchcoil series. These are wired the same as the F75/70 searchcoils but are electrically different. Even though some customers have tried searchcoils from one series on a machine designed for the other series and decided that they "work", the factory is not going to say that they "work' because we know there is performance degradation whether or not the customer knows (or even cares) about that.  (Dave Johnson) (emphasis mine)

Well, I care, but I sure don't know.

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Steve.....like you said,,,its a crap shoot.....but my little 4x6 F75 concentric didn't work on any of my 19 kHz models.   Sometimes the larger concentrics will work....but it seems as the concentrics get smaller they go into continuous overload. 

Good luck with it though.....you really never know until you try.

HH
Mike  

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2 hours ago, Chase Goldman said:

Other relevant threads:

Thanks for the reminder.  I seem to be repeating myself ever 6 months, but at least I showed pictures this time.  🥴

That official Tek-Fisher cross compatability chart is pretty conservative (consistent with something Dave Johnson said in the quote Steve posted to initiate this thread).  From what I see, except for one known clone (Tek Patriot = Fisher F70) the only coil that shows cross compatibility is the 4 inch coil designated for the F5 which works on the Greek Series as well as the 'new' (this will get Simon on a rant) F11/22/44 series.  Even the F19 and G2, G2+ show different coils than the Gold Bugs.  Very disappointing on First Texas's part, IMO, to not fill in this chart more completely with what is obvious to many of us.  Were they trying to hide the fact that the (lower MSRP) F19 and G2, G2+ are the same as (or even more feature rich than) the Gold Bugs?

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15 hours ago, GB_Amateur said:

Very disappointing on First Texas's part, IMO, to not fill in this chart more completely with what is obvious to many of us.  Were they trying to hide the fact that the (lower MSRP) F19 and G2, G2+ are the same as (or even more feature rich than) the Gold Bugs?

Manufacturer part number differences can simply mean a decal difference. I suspect that’s what happened here, since Gold Bug coils say “Gold Bug” on them. This is a compatibility chart, and it should show what coils work, but I can see how that could happen. The “will not interchange with other coils” asterisk only refers to hardwired coils, not electronic compatibility.

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One of my mate just bought that for his sons FakeGBug and the coil is fake too maybe 40 bucks...........

 

 

RR

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