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Other First Texas Model Coils On The Fisher F75


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(I moved the conversation over here since it was going off-topic.)

In the above thread, relicmeister mentions that he put the Teknetics Omega ("frat brothers") 5in X 10in DD coil on his F75 and it worked fine.  I expressed surprise and a motivation to try that out myself.  I can now confirm that my Fisher Gold Bug 5"x10" DD works on my F75.  I'm going to investigate further.  I have both 5" round DD and 7"x11" DD for both these detectors.  I'm curious to see if I can find any differences when mounted on the F75.  Different ground balance numbers?  Different TiD values?  Different sensitivity (depth)?  I also have an inductance meter so I'll make some measurements of the coils on the bench and see how different that important characteristic is.  This might shed some light on why to swap works.  Stay tuned.

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Dave Johnson on First Texas coil compatibility:

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.

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  • 1 month later...

I like to be able to use a concentric coil. I've always gotten on better with them and in mild soil they punch deeper than an equal sized DD. It's one reason I chose the F75 over the T2. The F75 can run both DD and concentric. The T2 can only run DD. It's something I like about the V3i/VX3. They are the only (simultaneous) multifrequency machines I'm aware of aside from older FT machines that uses concentric. Minelab along with many other companies have left concentrics behind.

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 All the 7.8 and 7.6 kHz coils work but only to a set signal strength. They are basically on and off coils.    Air tests to about 7 or 8 inches and then quick cut off.  No modulation.    I occasionally use the 11" Triangulated concentric coil on my F75LTD for a little concentric ground coverage.   Seems ok for the top 4 to 5 inches of ground.   I'd like to see one of these specifically for the F75 as I like that coil.

The new 7.8 kHz 4" concentric coil air tests good on the F75.  It will allow modulated audio to about 6-1/2 to 7".    Haven't used it in the ground yet.

I hear you Cipher on the V3.   I pretty much just use the 9.5 and 12" concentric on my V3 for the finer discrimination ability.   The DD's get better depth in my ground but I want the better discrimination I get from the concentric.

HH
Mike

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  • 3 weeks later...

I am starting to use it on my f75 in dense iron and it does work well though I did see a several TID points of difference from the stock elliptical coil. I'm not really concerned about that. I guess as Dave Johnson said it's Ok To try and won't harm the detector. 

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