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Yes, I dared to dissect one of my coils (it was the worst used one).
The reason was just to get all the possible data out of it before trying to set up a larger one, hopefully as sharp as the original.
(OK, I still have 4 spare coils to hunt with.)
There are some particularities (see additional notes).
Opening the plastic shells was simple, they were that worn out that they felt off.
A red-brownish paint was on the inner side of the plastic coil shells,
for shielding reasons presumably (but no visible direct connection to
ground/shield of the unit itself).
The coils themselves were epoxied and laid in a yellowish foam,
I guess urethane foam.
To deal with the epoxied coils themselves was a bit tricky and
it took some time to find a solution about how to dismantle them
without damaging the wires.
After some try outs with different solvents,
a solution was found to “solve” the epoxy (or urethane) in
“tri-chlor-ethane” C.2-H.3-Cl.3. I’ll call it TCE here.
Reserve:
TCE is inflammable and toxic, wear gloves, use organic vapor filter mask and
work under a good vent or in free air.
Watch and respect instructions on TCE container.
DO NOT SMOKE!
If you use TCE, it will be at your own risk.
In fact the epoxy compound was not solved but only softened enough to be peeled/scraped off.
After a 3 day maceration time I was able to peel off a layer of around 0,5 to 1 mm. This procedure was repeated around 8 to 10 times.
Here is the data: (All tests revealed same readings for each partial D of the entire coil.)
Type of metal detector:
Bounty Hunter (former PNI or Pacific Northwest Instruments)
IB 300 (coil fits the IB100 and IB200 too) from the mid 1970ies.
R = 3 R
L = 0,131 mH
C = 12,69 uF
cross section of wire:
0,25 mm ( that’s what my micro meter screw read, without the enamel it might be 0,22 mm)
turns per coil:
24 (counted on 2 cut sections for each coil)
length per turn:
+/- 47,5 cm
coil diameter:
19 – 19,5 cm (DD config & greatest single D extension)
cross section of windings:
2-3 mm
2 capacitors reading each 22 nF
particularities / additional notes:
- There was a circular piece of Aluminium around 29mm x 1,5 mm put atop the DD intersection near the 2 capacitors. Carl wrote once here on the forum that some brands used this technique to balance coils… or was it to null the coils?
- The epoxy or urethane compound seems to have been mixed up with some metallic powder, either Aluminium or Zinc. The compound is greyish and when cut, there appear some tiny shiny dots on the cut surface. Maybe a kind of shielding. One of the ground wires was directly inserted into this epoxy/urethane compound.
- However, the epoxy compound does not seem to be conductive. I tested on many test points with the R-meter and it seems there passes no current. This statement with reserve, as I have nothing for measuring minimum currents. Anyway, the solder points in the coil unit were not isolated, if the compound was conductive, there would have been shorts. The conductivity question seems to be answered.
- Considering that one “D” consists of two arc bows, one arc bow fits into a 20 cm diameter circle, the other arc bow fits into a 40 cm circle. This is maybe a ratio for constructing DD coils.
The dissection made possible to do the following drawing and to draw a schematic for an individual D coil.
Some may say that there is noting new.
Right, exception made for the figures and the 2 or 3 odds.
Anyway, some may find enough hints to start constructing a DD coil.
HH
Paul
The reason was just to get all the possible data out of it before trying to set up a larger one, hopefully as sharp as the original.
(OK, I still have 4 spare coils to hunt with.)
There are some particularities (see additional notes).
Opening the plastic shells was simple, they were that worn out that they felt off.
A red-brownish paint was on the inner side of the plastic coil shells,
for shielding reasons presumably (but no visible direct connection to
ground/shield of the unit itself).
The coils themselves were epoxied and laid in a yellowish foam,
I guess urethane foam.
To deal with the epoxied coils themselves was a bit tricky and
it took some time to find a solution about how to dismantle them
without damaging the wires.
After some try outs with different solvents,
a solution was found to “solve” the epoxy (or urethane) in
“tri-chlor-ethane” C.2-H.3-Cl.3. I’ll call it TCE here.
Reserve:
TCE is inflammable and toxic, wear gloves, use organic vapor filter mask and
work under a good vent or in free air.
Watch and respect instructions on TCE container.
DO NOT SMOKE!
If you use TCE, it will be at your own risk.
In fact the epoxy compound was not solved but only softened enough to be peeled/scraped off.
After a 3 day maceration time I was able to peel off a layer of around 0,5 to 1 mm. This procedure was repeated around 8 to 10 times.
Here is the data: (All tests revealed same readings for each partial D of the entire coil.)
Type of metal detector:
Bounty Hunter (former PNI or Pacific Northwest Instruments)
IB 300 (coil fits the IB100 and IB200 too) from the mid 1970ies.
R = 3 R
L = 0,131 mH
C = 12,69 uF
cross section of wire:
0,25 mm ( that’s what my micro meter screw read, without the enamel it might be 0,22 mm)
turns per coil:
24 (counted on 2 cut sections for each coil)
length per turn:
+/- 47,5 cm
coil diameter:
19 – 19,5 cm (DD config & greatest single D extension)
cross section of windings:
2-3 mm
2 capacitors reading each 22 nF
particularities / additional notes:
- There was a circular piece of Aluminium around 29mm x 1,5 mm put atop the DD intersection near the 2 capacitors. Carl wrote once here on the forum that some brands used this technique to balance coils… or was it to null the coils?
- The epoxy or urethane compound seems to have been mixed up with some metallic powder, either Aluminium or Zinc. The compound is greyish and when cut, there appear some tiny shiny dots on the cut surface. Maybe a kind of shielding. One of the ground wires was directly inserted into this epoxy/urethane compound.
- However, the epoxy compound does not seem to be conductive. I tested on many test points with the R-meter and it seems there passes no current. This statement with reserve, as I have nothing for measuring minimum currents. Anyway, the solder points in the coil unit were not isolated, if the compound was conductive, there would have been shorts. The conductivity question seems to be answered.
- Considering that one “D” consists of two arc bows, one arc bow fits into a 20 cm diameter circle, the other arc bow fits into a 40 cm circle. This is maybe a ratio for constructing DD coils.
The dissection made possible to do the following drawing and to draw a schematic for an individual D coil.
Some may say that there is noting new.
Right, exception made for the figures and the 2 or 3 odds.
Anyway, some may find enough hints to start constructing a DD coil.
HH
Paul
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