The Crossbow Classic PI

[TowySalmon]

W=192mm, or as far as I can see, 7 9/16". The measurements were made with coil cover on so please take the thickness of that into consideration. Thickness of plastic on spare cover is 1mm, so without cover it would be 190mm.

[6666]

TowySalmon would you mind measuring the outside dimension of one of the coils ellipses please
as per attachment you will see the arrows point to the measurement I'm asking about thanks.

[6666]

So clearly it's not a DD coil after all.

The coil plug wiring is as follows:
L1 263uH (6R6) coil between pins 1 and 2
L2 706uH (7R0) between pins 2 and 3
pins 1 and 5 connected together
pins 3 and 4 connected together

Obviously, with pins 1 and 5 shorted together, the coil plug wiring is connecting the coil as a mono with L1 and L2 in series. Effectively this means the detector "sees" a mono coil with 439uH, requiring a 330R damping resistor between pins 4 and 5.

Thanks for this surprising info, glad you got it to work , interesting that this butter fly coil configuration gives 439uH with those two coils in series.
Given that it is such a large coil, and in the short amount of testing, did you see any advantage over a real round mono ?

[Qiaozhi]

Also, I did try and use the SEF coil as separate TX and RX loops, but it was hopeless. The loops are not balanced (unlike the Garrett Infinium coil) and the sample delay was at 35us. Detection was abysmal, with coins only being detected at 3" to 4". Clearly, it's intended to be connected in mono mode, which incidentally removed the need for an adapter cable.

[Mega B]

I own and use one of the 'original' Crossbow machines and is No13 out of the original batch that had been made,still in exactly the same condition as when it was made,wont ever sell it for sure as its such a rare beast.

The coils that i use are the stock 10.5'' Mono and the Garrett SeaHunter Mono coils that George has mentioned about ie 14x10 and 8'' Mono's,the smaller 8'' coil stays on the machine almost all the time.The larger Garrett coil does go deep for sure,i have a spare new Detech 18'' Mono from a GPX that is sitting around gathering dust so i may and try and see if that works on the Crossbow without altering anything,the main reason being is that i also use that 18'' coil on my TDI Pro which does work reasonably well.

The Crossbow is a very rare machine and the original ones very rarely come onto the market,the original batch run was for just 12 machines but No13 which i have was a spare machine that George built for me.Ideal machines for deep relic or hoard hunting but if you you are looking for fine gold jewellery or nugget hunting then not the best machine for the job,i also lucky enough too own a Mirage Pulse for fine gold jewellery and a TDI pro for deep hoard hunting.

[Qiaozhi]

It turns out that the Detech SEF coil is rather unusual. Initially it was assumed that the coil was a DD type, which was quite reasonable as Detech advertise it as such. However, the cover of the box says:
-----------------------------------------------------------------------------
The double elliptical coil with Symmetric Electro-magnetic Field
is the best performance coil.
Compared to the Double D coils it has the following advantages:
- better ground balance
- more stable operation
- deeper in the ground
- better pinpointing
- more accurate target identification
-----------------------------------------------------------------------------
So clearly it's not a DD coil after all.

The coil plug wiring is as follows:
L1 263uH (6R6) coil between pins 1 and 2
L2 706uH (7R0) between pins 2 and 3
pins 1 and 5 connected together
pins 3 and 4 connected together

Obviously, with pins 1 and 5 shorted together, the coil plug wiring is connecting the coil as a mono with L1 and L2 in series. Effectively this means the detector "sees" a mono coil with 439uH, requiring a 330R damping resistor between pins 4 and 5.
What's interesting is that a mono coil is sensitive from edge to edge, whereas the SEF coil is sensitive across the overlapping section of the two loops. Hence it reacts like a DD coil, but with the advantages of a mono.

In a way, this setup is similar to a White's Dual Field, but in a Butterfly (DD) format. Although, in this case, it was possible to critically damp the coil with one resistor.

[TowySalmon]

A huge thanks to Qiaozhi for all his time, patience and expertise. A thank you too to all the others here who have contributed their help.
The Crossbow now works with the new coil, but I do not have the knowledge to explain what the problem with the wiring was.

[6666]

Dont leave us in suspense we are all dyeing to find out if this was fixed and what was the problem with the wiring ?

[TowySalmon]

I have replied via PM.
Thank you.

[Qiaozhi]

Hi all,
Well, we installed the jumpers between 1&2 and 3&4 at the box end plug of adapter and checked the connections twice with ref' to the diagram. Funnily enough, I had coloured the connections on drawing very much the same as your revised .pdf. The correct plugs have been used and the layout of pins is now imprinted on my brain as I have looked at them through a magnifying glass so many times.
So, picture of coil label and for interest my coloured lines on drawing.
[ATTACH]40952[/ATTACH]

[ATTACH]40953[/ATTACH]
And did it work when we attached the (finally) correctly made adapter? No. There is no response from the coil whatsoever?

Whereabouts in the UK are you located?

[TowySalmon]

Hi all,
Well, we installed the jumpers between 1&2 and 3&4 at the box end plug of adapter and checked the connections twice with ref' to the diagram. Funnily enough, I had coloured the connections on drawing very much the same as your revised .pdf. The correct plugs have been used and the layout of pins is now imprinted on my brain as I have looked at them through a magnifying glass so many times.
So, picture of coil label and for interest my coloured lines on drawing.


And did it work when we attached the (finally) correctly made adapter? No. There is no response from the coil whatsoever?

[Qiaozhi]

I obviously cannot read the schematic. To my eyes and common sense, the connections to 1&2 and 3&4 are to the left of the adapter, which is to my way of thinking, the plug inside the control box. But hey ho. I will get pal to connect 1&2 and 3&4 on the plug that is at the end of adapter that connects to control box.

Also!!!! I think I mentioned this previously, everything connected to all. The schematic shows the GPX coil plug as having continuity between 1&2, 3&4, 4&5.
On my coil plug, it's 1&2, 1&3, 1&4, 1&5, 2&1, 2&2, 2&3, 2&4, 2&5, 3&1, 3&2, 3&3, 3&4, 3&5, 4&1, 4&2, 4&3, 4&4, 4&5, and yes, you've guessed it, 5&1, 5&2, 5&3, 5&4,
So, I won't be putting any money on things working tomorrow.

OK - let's see if I can make this a bit clearer. Please see modified PDF attached.

In the bottom diagram, everything on the left of the adapter cable is in the Crossbow enclosure, and everything on the right of the adapter cable is in the Minelab coil connector. The connections shown in the middle (between the right and left connectors) are in the adapter cable. The idea of the adapter cable is to connect the Minelab TX and RX loops to the correct pins on Crossbow, and to connect the damping resistor in the enclosure across the TX loop. When the adapter cable is disconnected, the resistor is out of circuit. If you then connect the original mono coil (obviously without the adapter cable), it uses its own internal damping resistor.

Hope this makes sense.

[6666]

I obviously cannot read the schematic. To my eyes and common sense, the connections to 1&2 and 3&4 are to the left of the adapter, which is to my way of thinking, the plug inside the control box. But hey ho. I will get pal to connect 1&2 and 3&4 on the plug that is at the end of adapter that connects to control box.

The pins should have numbers beside them on the plug front and back, so the pin number is the same weather you are looking at them from the front or back of plug.
The plug is also a 5 pin microphone plug NOT a 5 pin DIN.

[6666]

It is for the GPX, GP, SD series: https://detech-metaldetectors.ro/en/...lab-gpx-series

I do though fear that after doing continuity that something is not right...........?

What exactly is written on the coil label ?

[TowySalmon]

I obviously cannot read the schematic. To my eyes and common sense, the connections to 1&2 and 3&4 are to the left of the adapter, which is to my way of thinking, the plug inside the control box. But hey ho. I will get pal to connect 1&2 and 3&4 on the plug that is at the end of adapter that connects to control box.

Also!!!! I think I mentioned this previously, everything connected to all. The schematic shows the GPX coil plug as having continuity between 1&2, 3&4, 4&5.
On my coil plug, it's 1&2, 1&3, 1&4, 1&5, 2&1, 2&2, 2&3, 2&4, 2&5, 3&1, 3&2, 3&3, 3&4, 3&5, 4&1, 4&2, 4&3, 4&4, 4&5, and yes, you've guessed it, 5&1, 5&2, 5&3, 5&4,
So, I won't be putting any money on things working tomorrow.