Gold Century GC-1018, GTX9055, L23BK

[aoma]

thank you

[sido]

Thanks Jan for the further info

The free small black wire is connected to the shield of the cable and terminated with the 2 brown wires.

The receive resonance frequency calculated is 6.44Khz. That sounds about right.
The transmitter resonance frequency calculated is 6.24 Khz. Close to your frequency measured pickup coil, but to close for my liking to the RX frequency, unless the R&D design goals were to match both TX/RX for same operating resonance frequency.
Some detectors are designed like that, but the norm is to have both TX/RX seperated by a marginal distance.
The LP filter cutoff frequency from your frontend circuit is 8.00 Khz.

Now this coil is starting to look different compared to my specs, but the frequency of operation and idea is the same.

Much appreciated for posting the circuit and coils. I still have to compare the rest of the circuit and get around to making a smaller coil to suit.

Will keep you posted with my findings.

BTW, have you attempted to make a new coil for your detector based on your coil parameters??

Cheers Sid

[jan w]

Hmm, I must have made a mistake with the measurement off the coils, it did not match with the frequency.
I measured it again bud now from the outside, the coil is put together and can not be opened easily.

Frequency with a pickup coil is 6250Hz
calculated the Tx coil ± 1,25mH
Rx coil I measured ±1.3mH

[sido]

Hi Jan, thanks for posting the makeup of the inner coils. I have been wanting a Picture of the insides to get a picture of how the Chinese go about producing these coils.


Something does not add up. I put these values in a Frequency calculator and cannot seem to get the resonance frequency of around 6.7Khz for TX.


Do you have this coil still open and if so would you mind re-posting the parameters as in the picture below.
I want to build smaller and larger coils for these 6.7khz detectors and post my findings.


I cannot open my coil as it is still working great after 5 years, so if you can supply more info, it will assist me to have a fair idea how to approach in making of different sizes coils.


Also measure the Resistance at the Inductance points referred below in Picture and see where the RX copper wires connect on that small PCB. I think they may be underneath on the Red/Black wires.
Much appreciated.


Cheers Sid

[jan w]

Does your unit operate in the 6.7 - 6.9 Khz range? and if so are you able to measure the Inductance across TX and RX on the connector coil? Two left pins and 2 right pins (either would be TX or RX). The Tx oscillator is identical in circuit design layout but i see some resistor values different to yours. Have to check the resonant Capacitor on mine and compare it to yours. Would say your's operates in the same 6-7Khz range.

Yes it does.
I had ones to open the disc, be coarse of a bad connection between the shielding and the ground wire, then lucky me, I measured the coils and took some pictures
The inner coil was 2.2mH and the outer coil 1.8mH and between a small coil from 6.6uH from the outer to the inner coil
But there are some capacitors inside, 470nF + 47nF // on the outer coil and there was a small capacitor 470pF from the outer to the inner coil.

[sido]

The first OP-amp LP filter of your schematic has a frequency cut-off at 8.00khz.

Therefore can assume its a VLF with TX frequency of 6.5-7.0 Khz.

All these Chinese units seem to operate around those frequencies.

Cheers Sid

[sido]

Hi Jan, thanks for the better Resolution.

The picture of your detector is the previous model with bells and whistles which complicated things.

The detector i am refering to is the simplified version below from what i see so far. With the higher resolution schematic posted now i will compare the two soon. As for similarities, like i posted previously, so far are almost identical. Will look at the comparators and audio section and post back.

Does your unit operate in the 6.7 - 6.9 Khz range? and if so are you able to measure the Inductance across TX and RX on the connector coil? Two left pins and 2 right pins (either would be TX or RX). The Tx oscillator is identical in circuit design layout but i see some resistor values different to yours. Have to check the resonant Capacitor on mine and compare it to yours. Would say your's operates in the same 6-7Khz range.

The transistor pre-amp is the same design but op-amp has ben replaced with TL064 instead of LF411. Still identical circuit design, just different component values. I have modified the frontend which has made it into a super sensitive detector now without any compromise to other circuitry.

My unit has all that wax stuff on some ic's and components, so will have to remove it to identify further similarities.

The version GC/MD1023 is considered the best performer of all the Chinese variants and i can agree to that, for the fact i can run this detector on highly mineralised soils with no ground effects/emi/rfi interference at all on soils considered the worst you could find anywhere around the world. And that is here in Australian/Victorian Goldfields.

Have found many relics and coins with it too.

Cheers and thanks for the schema.

Sid

[jan w]

Hmm, the image was not click-able , Yes I have a larger resolution schematic, it is here:

http://postimage.org/image/t9sa6up4f/full/

schematic made with ExpressPCB

schematic file: http://speedy.sh/GV9DU/1018-a.sch
I have not all the values from the resistors and capacitors, during the drawing from the schematics i discovered that they use mostly values 1, 2, 5, = 20% step
much room for improvement , and some resistors need to be removed from the board for good measurement, and that i did not want to do that.

I also discovered it did not detect gold in the Disc mode , it turned out that RV4 was not correct adjusted, setting now is close to 0 ohm
The threshold setting on my detector do not work, or at least i do not see or hear any difference on the settings, wrong values on the board, Chinese mistake i don't now.

Feel free to make make any improvement on this detector, it can be a lot better

this is the detector we are talking about:

[sido]

Gold Century Chinese detector gc1018 also known as GTX9055 and L23BK

Hi Jan w, I almost missed this post of yours.

Thanks for taking the time to trace the GC1018.
This circuit is very similar to the GC1023/MD1023 also known in Australia as the Goldsnoop.
There are some frontend mods that can be changed on the pre-amp for a little bit of extra sensitivity if it already lacks it.

Do you have a higher resolution schematic?? There is NO known Goldsnoop schematic and your GC1018 is almost identical, but cannot verify due to low resolution schematic posted. One or two IC's have been eliminated and transistors have been put in place as switching devices.
Frontend op-amp is replaced from LF411 to TL064. Demod the same. Tx oscillator the same......I am interested how they removed the Threshold pot from your model GC1018 to later GC1023/MD1023.
Bernte-one and a few others would be interested in this schematic.

Much appreciated, thanks

Cheers Sid

[jan w]

Gold Century Chinese detector gc1018 also known as GTX9055 and L23BK