I didn't need another project -

[6666]

The part in the red box is purely a flexible shaft coupler. The primary seal is the ring which sits in a groove within the top plate to the left of the red boxes. The 1/4in shafts from the knobs and into the couplers are stainless steel, but it does not matter what metal the actual pot and switch shafts are made of. Could even be plastic. There is an additional seal between the control knobs and the outer surface of the top plate which consists of a nylon washer under the knob and an O ring against the top plate surface. How the O ring groove in the top plate holes are machined I do not know. It also appears that those three O rings are square section.

Eric.

Those flexible shaft coupler's are also used on 3D printers if you search on ebay on
"3d printer couuplings" you will find lots of all sorts and cheap, you can drill them out to match the pot shaft.

[Ferric Toes]

Thanks Mr. Eric.
I'm not shure, but isnt it be a good for future modifications to lower feedback resistance say to 100k and compensate overall amplification at dc amplifier by x10.
Just so good op amp and feedback resistance is not optimised for it noise performance.

I fully agree. I am going to remove all the Rx IC's and replace them with sockets so that better devices can be used. If possible, I might rewire the OPA37 to take a dual opamp. This would help optimise the front end better. I certainly want to bin the 741.

Eric.

[Ferric Toes]

Where can I find these waterproof potentiometer shafts? Looks to be a standard part I have the same on the JW Fishers 8X.

The part in the red box is purely a flexible shaft coupler. The primary seal is the ring which sits in a groove within the top plate to the left of the red boxes. The 1/4in shafts from the knobs and into the couplers are stainless steel, but it does not matter what metal the actual pot and switch shafts are made of. Could even be plastic. There is an additional seal between the control knobs and the outer surface of the top plate which consists of a nylon washer under the knob and an O ring against the top plate surface. How the O ring groove in the top plate holes are machined I do not know. It also appears that those three O rings are square section.

Eric.

[eclipse]

Where can I find these waterproof potentiometer shafts? Looks to be a standard part I have the same on the JW Fishers 8X.

[Vadim18]

Thanks Mr. Eric.
I'm not shure, but isnt it be a good for future modifications to lower feedback resistance say to 100k and compensate overall amplification at dc amplifier by x10.
Just so good op amp and feedback resistance is not optimised for it noise performance.

[kt315]

For KT315, sheet too large for my copier and out of date with 3055 TX and 709RX.
---
thank you. you can hang up the sheet on vertical wall, choice a sunny day and camera has to be >12MP. i did so. vertical wall was a bus stop.

[Ferric Toes]

Two jobs done so far. First was to change the 7 cell Nicad pack for something better and lighter. Now I use 3 Li-ion cells which are half the weight and much bigger capacity. I've used protected cells to avoid draining them if the detector is inadvertently left switched on. Charging circuit needs to be changed too. The electronics at the moment draws 150mA so the added capacity will allow running at a higher rep rate to speed up the response which is a bit slow at present. TX pulse width is 200uS so I will look at increasing that too. Mosfet will be changed for one with a lower Rds.on and a series diode. I will remove the IC's from the RX chain and put in sockets so that alternative devices can be tried. Several other things could be changed but this will do for the present. Oh yes, I changed the twisted wires from the coil socket to a miniature coax. The problem with this case is that the connector is on the bottom and very close to the pcb pads for the coil. To withdraw the electronics for testing then requires a long internal cable if the same connector is to be used.

For Vadim18 input resistor 1K and feedback resistor 1000K for OPA37. For KT315, sheet too large for my copier and out of date with 3055 TX and 709RX.



Eric

[Vadim18]

Quite impressive opamp for 1989, with great noise and bw performance. I guess in the XL500 detector opa37 should have feedback resistance less than 1000kOhm.

[Ferric Toes]

I believe it is made about 1987

[ATTACH]53232[/ATTACH]

You are not far off. I found a QC date stamp on the chassis - 15th March 1989. That explains the upgrade to a Mosfet and the OPA37.

Eric.

[kt315]

I believe it is made about 1987

[ATTACH]53232[/ATTACH]

perhaps Melbeta. do not remember who made a list.

[Xtrem]

I believe it is made about 1987

[Ferric Toes]

I found that the XL-500 works after all without any repairs needed. I thought there were no TX pulses, but with the board out of the box all is OK. TX transistor is a Mosfet RFP8N18L. RX line up is OPA37; Jfet gates 2N5566, integrator CA3140, d.c. amp. 741. There is also a LM358 and a CA3290. Not sure what the latter does at the moment. All voltages and pulses appear OK, although not accurately measured at the moment.

Serial no. leads me to believe it is 1973 production, but anyone familiar with Garrett numbering could perhaps confirm this.



Eric.

[surfdetector]

Got one for 100€ without battery. It is on the way.

That seems like a good price. I will be interested to hear how well it works.
Cheers

[kt315]

I have an original production schematic from Garrett
---
Eric, if be honestly, did you project this schematic? pleasure.

[Vadim18]

Nice and fun project. Will be interesting to see performance before and after upgrades.