Vallon VMH3CS Mine Detector

[Ferric Toes]

Hi Eric
Here is one on eBay that shows a punched date of 7/2006.
Chet

http://www.ebay.com/itm/201580006429...%3AMEBIDX%3AIT

Yes, that is the label I was looking at. Interesting that the 2006 model does not have the 'pinpoint' button.

[Ferric Toes]

Eric,

Your use of Scotch 24 is very good to see as I discovered this stuff many years ago when doing independent coil research. Lead shields seems to have fallen into safety and health issues these days. I see that you chose to spiral wrap the double layer Scotch 24 around the coil. Another method is to cut it in a single layer a bit narrower than the coil cross section bundle circumference and put it on the coil as a U-shaped shield with the open seam on the top of the coil. This keeps the wire mesh shield from forming a shorted cross section loop around some coils that may be detected at low delays. I used this U-shaped shield method along with Teflon insulated coil wire for an 11" 300 uH coil used on your CS6PI low power PI design that I modified to operate at 13.5 KHz at about a 7.5 uS delay. This gets me about 14" on a U.S. Nickel. The spiral wrap shield method, however, may not be an issue with this VMH3CS mine detector coil where low noise and not coil speed is the main issue.

Thanks for the update.

Joseph J. Rogowski

This is the first time I have used the Scotch 24 tape. It looks as though the Vallon coil has it spiralled around from what I could see by scraping off the potting in a dud coil. Doing the same gave the best chance of ending up with a working coil. The manual says that the unit checks L, C, and R of the coil on power up.
I re-measured the resonant frequency as my earlier measurement did not take into account the capacitance of the coiled cable inside the telescopic part of the shaft. This alone adds an extra 290pf to the coil and cable in the lower shaft. The Vallon coil with total cable measured 156kHz and my 11inch coil was 153kHz. Since my coil works, this difference must be acceptable.

A U shaped shield of the Scotch 24 must be difficult to hold in place. I have always used total wrap round, even on fast coils, as the collapsing magnetic field on switch off does not induce eddy currents in a concentric shield. On the other hand flat shielding does have eddy currents so you have to use thinner conductive material.

[Chet]

Mine has the year 2010 on the serial no. plate. There is also a 5 and a 10 punched on a final inspection label, so could be May 2010.

Hi Eric
Here is one on eBay that shows a punched date of 7/2006.
Chet

http://www.ebay.com/itm/201580006429?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

[Chet]

when you tested with US nickel was that with ground balance on ??? if so what is the depth on nickel with ground balance switched off ???

Hi Daverave
The Ground Balance was off. The test was in my back yard with the coil lying on a 1.5” thick board lying on low mineralized ground. The 1.5” represents the average scan height over cobbles, pine needles, leaves and branches encountered in the California gold country. I just retested by ground balancing beside the board (at 7 on the control) then placed the coil back on the board. It surprised me that it only lost 0.5” in depth. I know that is loses much more when on high mineralized ground in the field.
Have a good day,
Chet

[Ferric Toes]

Hi Eric, Carl
The VHM3CS has been in production for many years. Do your units have manufacturing dates on them? The date may be on an inspection seal. The one that Carl has may be an earlier model or an earlier software version.
Have a good day,
Chet

Mine has the year 2010 on the serial no. plate. There is also a 5 and a 10 punched on a final inspection label, so could be May 2010.

[daverave]

Hi Eric, Carl
I just tried a US Nickel with My White's TDI-SL with the 12" Dual Field Coil. It gets it solid sound at 9.5" and an iffy sound at 10.5". The VHM3CS has been in production for many years. Do your units have manufacturing dates on them? The date may be on an inspection seal. The one that Carl has may be an earlier model or an earlier software version.
Have a good day,
Chet

when you tested with US nickel was that with ground balance on ??? if so what is the depth on nickel with ground balance switched off ???

[bbsailor]

Today, I thought I would have a go at making a 11in coil for the VMH3CS. I used the same gauge wire and found that 50 turns gave a similar inductance to the standard truncated ellipse coil. I then overwound it with PTFE tape and then helical cable wrap to space off the shield. The shield is Scotch 24 tinned copper shielding and this went on quite smoothly when I anchored the end with tie wraps.
I had a spare bottom shaft and connected the coil to the internal cable. This is where I thought failure was going to spoil the day, as the detector signalled a fault. I put the scope across the coil wires and nothing was there. I then checked the continuity of the internal cable in the shaft. That was the problem. The shaft has a six pin connector and when I removed this, the cable was totally disconnected. Someone had tried to unscrew the connector and twisted the cable to the point where it completely broke. This took a while to fix, but when the coil was reconnected everything works fine. Great range, very stable - success. The next problem is purely mechanical: mounting the huge swivel assembly onto the coil shell. This has already been cut off a dud Vallon coil and it looks as a bit more work on the mill will be needed. The swivel is very good though as the cabling is internal and sealed. Just the job for shallow water hunting.
[ATTACH]36214[/ATTACH]

[ATTACH]36215[/ATTACH]

Eric,

Your use of Scotch 24 is very good to see as I discovered this stuff many years ago when doing independent coil research. Lead shields seems to have fallen into safety and health issues these days. I see that you chose to spiral wrap the double layer Scotch 24 around the coil. Another method is to cut it in a single layer a bit narrower than the coil cross section bundle circumference and put it on the coil as a U-shaped shield with the open seam on the top of the coil. This keeps the wire mesh shield from forming a shorted cross section loop around some coils that may be detected at low delays. I used this U-shaped shield method along with Teflon insulated coil wire for an 11" 300 uH coil used on your CS6PI low power PI design that I modified to operate at 13.5 KHz at about a 7.5 uS delay. This gets me about 14" on a U.S. Nickel. The spiral wrap shield method, however, may not be an issue with this VMH3CS mine detector coil where low noise and not coil speed is the main issue.

Thanks for the update.

Joseph J. Rogowski

[Chet]

I checked a US nickel on my VHM3CS and get an air range of 15 inches for a definite response and 16 inches for an iffy response that you would likely miss. I think that is good for a coil which is about equivalent to an 8 inch diameter. That is why I want to make a 12in and see what I get then. What foil are you using, Carl? Is it baking foil?
I hope to get another VHM3CS shortly, which I will be happy to open up and look at the works.

Hi Eric, Carl
I just tried a US Nickel with My White's TDI-SL with the 12" Dual Field Coil. It gets it solid sound at 9.5" and an iffy sound at 10.5". The VHM3CS has been in production for many years. Do your units have manufacturing dates on them? The date may be on an inspection seal. The one that Carl has may be an earlier model or an earlier software version.
Have a good day,
Chet

[Ferric Toes]

very nice workshop

That is just one corner, the rest was too untidy to show. I always get in a mess when working on something interesting. The big tidy up comes tomorrow.

[WM6]

When I grow up, I'll have such a workshop of my own.

Probably fertilization is poor to grow up faster.

When asked in quiz, I would say that it is workshop of our valued member Mechanic.

[Davor]

When I grow up, I'll have such a workshop of my own.

[Monolith]

very nice workshop

I would trade all my secrets for a workshop like that.

[green]

Did a simulation in spice. Don't know if it means anything since I couldn't enter coil diameter. Compared to coils, 300uH(1MHz resonance) and 1.5mH(170kHz resonance). Target TC 3.3usec which could be close to a .3gm nugget. Could see target decay on both simulations. Tested a 6x6mm piece cut from the bottom of an aluminum coke can(TC=3.1usec) and a piece 6x6mm cut from the side(TC=1.3usec) awhile back. Couldn't see the target decay on the 1.5mH coil simulation with a target TC of 1.3usec.

[daverave]

very nice workshop

[Ferric Toes]

Today, I thought I would have a go at making a 11in coil for the VMH3CS. I used the same gauge wire and found that 50 turns gave a similar inductance to the standard truncated ellipse coil. I then overwound it with PTFE tape and then helical cable wrap to space off the shield. The shield is Scotch 24 tinned copper shielding and this went on quite smoothly when I anchored the end with tie wraps.
I had a spare bottom shaft and connected the coil to the internal cable. This is where I thought failure was going to spoil the day, as the detector signalled a fault. I put the scope across the coil wires and nothing was there. I then checked the continuity of the internal cable in the shaft. That was the problem. The shaft has a six pin connector and when I removed this, the cable was totally disconnected. Someone had tried to unscrew the connector and twisted the cable to the point where it completely broke. This took a while to fix, but when the coil was reconnected everything works fine. Great range, very stable - success. The next problem is purely mechanical: mounting the huge swivel assembly onto the coil shell. This has already been cut off a dud Vallon coil and it looks as a bit more work on the mill will be needed. The swivel is very good though as the cabling is internal and sealed. Just the job for shallow water hunting.