Pim Puls .XR 7

[KingJL]

Some comments were made earlier about the coil damping and the lack of a resistor connected directly across the coil. It is a long time ago to recall, but I am sure there is no actual resistor inside the coil housing. What I am sure of, and which I remember surprised me at the time, is that the coil was wound with enamelled single core wire. The wire gauge was such that cross-sectional eddy currents were themselves having a damping effect and this was observed when I tested a coil on one of our other PI detectors at the time. There was no shielding in the coil.

I believe what is happening is that the damping path above D3 threshold is R5 and D3. Below D3 threshold the damping path becomes R5, R6, base-collector of the input transistor. At the D3 threshold transition point the gain of the preamp is squeezed to an extremely small value thus providing a relatively high impedance to this path, hence you can see slight ringing at this point. As the conduction of the input transistor ramps up, this input impedance decreases, providing a damping path and the ringing stops. A very elegant concept!! This just my opinion based on observation of the simulated circuit performance.

I wonder if a Vallon VMH3CS coil would work in this circuit? It has 1.5mH inductance, 3.4 ohms and 0.53mm solid enamel wire. Perhaps it would even work with a mosfet.

At that inductance, I feel confident that it will work with even an IRF740 (coss 330-350 pf). With the coil inductance at 780 uH, simulations indicate instability at anything more than 140 pf for coss.

[green]

I believe what is happening is that the damping path above D3 threshold is R5 and D3. Below D3 threshold the damping path becomes R5, R6, base-collector of the input transistor. At the D3 threshold transition point the gain of the preamp is squeezed to an extremely small value thus providing a relatively high impedance to this path, hence you can see slight ringing at this point. As the conduction of the input transistor ramps up, this input impedance decreases, providing a damping path and the ringing stops. A very elegant concept!! This just my opinion based on observation of the simulated circuit performance.At that inductance, I feel confident that it will work with even an IRF740 (coss 330-350 pf). With the coil inductance at 780 uH, simulations indicate instability at anything more than 140 pf for coss.

I think the op amp tries to keep the inverted input at +input value, if the op amp is fast enough you don't need a damping resistor other the input resistor. Maybe wrong. Don't know if the amplifier is fast enough in this case.

[green]

I think the op amp tries to keep the inverted input at +input value, if the op amp is fast enough you don't need a damping resistor other the input resistor. Maybe wrong. Don't know if the amplifier is fast enough in this case.

Was thinking op amp needed to be fast. Tried changing C1 in spice simulation. Slower amp just took longer to damp to zero volts.

[Ferric Toes]

While on the subject of XR##, there was a question some years ago on this forum as to who designed and made the XR6. Initially it was made by Geo-Electronics Ltd, which was my first UK business in 1970. When I moved to southern Ireland in 1975 and formed Location Technology, I continued the production for a while and later replaced it with a detector called Deepscan. Both of these models were sold to A-S in Germany who labeled them as Sniffer XR6. The electronics is quite different to the XR7 and XR71

Eric

[andon80]

Hi friends xr7 original PBC or Lay has done the drawinghere you can share

[Ferric Toes]

Does anyone have a schematic for the original XR7 detector? Also a diagram of what controls, switches, etc etc, are wired to the various pins. I have a complete and unused circuit board and would like to power it up and get it working with a coil.

Thanks in advance for any help.

Eric.

[Xtrem]

may be this can help

[Xtrem]

Sorry ,i dont have the detector anymore in my hands

[kt315]

maybe that i do not sure know

[kt315]

[eclipse]

Eric, I belive this is what you are looking for

DBP 2010 full.part1.rar
DBP 2010 full.part2.rar

[Orbit]

[Ferric Toes]

[ATTACH]42208[/ATTACH]
[ATTACH]42209[/ATTACH]
[ATTACH]42210[/ATTACH]
[ATTACH]42211[/ATTACH]
[ATTACH]42212[/ATTACH]

Sorry ,i dont have the detector anymore in my hands

I'm afraid the attachments don't open. Your pictures are very useful though.

Eric.

[Xtrem]

Sorry, now its ok

[kt315]

[ATTACH]42220[/ATTACH]
[ATTACH]42221[/ATTACH]
[ATTACH]42222[/ATTACH]
[ATTACH]42223[/ATTACH]
[ATTACH]42224[/ATTACH]

Sorry, now its ok

please read my opus for a future http://www.geotech1.com/forums/showt...here-share-out