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F75 Observation

T

Treasure-Hunter

New member
I recently returned from an 8 day hunt which was mostly in wheat stubble. I am a great fan and supporter of the F75 so naturally I chose to start out using it instead of one of my other machines that I had stubble bashed with in prior years. I noticed immediately that I was unable to even touch the top of the stubble without getting false signals and the falsing was terrible if I forced the coil through it in order to work closer to the ground. The performance was bad enough that I gave up on the 75 and resorted to a more stable, less powerful older machine I had with me. Never having had a problem with the 75 before when working brush and rough grass, with the exception of an occasional hard bump that made a false signal, I was a bit concerned my shielding had failed on my coil. When we returned home I decided to take the coil cover off as I was cleaning things up and there was about 1/2 teaspoon of dirt between the coil and cover. I have heard for years that sometimes this can cause erratic behavior but it is an easy thing to forget to do. Anyway, to make a short story long, I took the 75 out to some brush, worked it pretty rough and guess what... quiet as a mouse even at high sensitivity. Apparently the 75 is very sensitive to the movement of the dirt particles in the tiny air gap between the coil and cover when being bumped or jarred in rough hunting conditions. Sorry for the long post, thought this might help some with their noise issues.
HH Jim
 
There IS a Simple cure which i`ve used for years ! Silicon mastic !
Buy a Tube from your Local D.I.Y Store and then remove the Coil cover . Cut a small Bit off the Pointed Nozzle of the Applicator to your tube Of mastic. (Bathroom Sealant mastic is ideal) You`ll need to only cut a small bit off to cause a "thin" bead around the Edges of the F75 coil cover . Very carefully (with this Shape especially) proceed to Go all around the leading edge of the Coil cover trying NOT to make a break in the line of the bead.
Go all around, and when finished lay the coil cover either on the floor and Proceed to drop the coil onto the coil cover and enable the coil cover to be completely inserted onto the coil. Press down firmly to press out any air gaps that may form. Look around the edges and with whetting your finger with spit or water blend the Mastic to form a neat seal around the edge of the coil cover to coil. Wipe any excess Mastic off with a cloth moistened with White Spirit.
Let stand for 24 Hours. Your coil is now sealed to sop any further Dirt or Possible Mineralised Grit getting between your coil cover and your coil . If you ever want to remove the Coil cover Slit seal edges with a Micro thin Blade of a craft knife. And work loose. Job Done !
 
With mastic/caulk you will eventually get a crack and the fine sand will get in and then you will have a big problem
The best way is to use marine epoxy and coat the coil and slightly up the sides. Use masking tape so it Will look neat and professional.[attachment 67395 wot.jpg]
 
erikk,
I put marine epoxy on all of my coils at the start of this year. It works great and I have not had to deal with coil covers again.
HH, B Spa
 
Sorry to disagree ,Erikk, but that is not necessarily true. If you use a Bog standard Mastic yes, that what you say may well be true, but if you use the "Expandable type" as used in the Waterproof Bathroom sealant mastic ,it will do what it say`s and expand to movement, and therefore will NOT crack.
I have used this type for many years since silicon mastic first came out, and i`ve NEVER had a coil cover to Coil sealed with Bathroom Mastic Crack on me yet. On every detector I`ve ever used it on.
I do not doubt for a second the marine type you use is a very good type . all i`m saying is the bathroom type you can buy at any D.I.Y stores will be probably much cheaper and as effective as Marine type mastic if you make sure when reading on the label that it does stipulate "expandable" type .
 
that they are saying if you use the marine epoxy, you don't need a coil cover. Is that correct? Just apply thr epoxy to the coil and be done with it?

J
 
Well I don't know about expandable but the bath caulk I used on my Excal did develop cracks and did let in the fine sand.I just found it simpler to use epoxy and be done with it so I did all my coils that way
 
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