Tesoro Lobo news

[porkluvr]

First change the 15nF on the TX to 10nF. This will give you 20.5kHz. which should be close enough. As a "calculated guess", I would also replace the 4n7 cap on the RX with a 10nF. If the residual voltage and phase are incorrect, then try adding a few pF across the RX cap until you get the right values.

As porkluvr says, you'll really need a scope to do this properly.

AND we also need to see the exact same schematic as what you are working from and know about any deviations from what is shown, otherwise we are just barking at the MOON.

edit: Maybe I should speak for myself. I didn't mean we, I meant me. I would really like to see what you have built before I try to tell you how it should be modified. I mean, there are about 5~8 different versions of Lobo "clones" floating around. Which schematic did you use?

[Legaucho]

Many thanks Qiaozhi andporkluvr for your answers rich in interest.

I wil try this evening the capacitors change.
Concerning the Fisher coil I made an extension cable to be similar with the connection on the Lobo.

I use this schematic http://www.geotech1.com/forums/attachment.php?attachmentid=18453&stc=1&d=13289041 55
It's a pity for me because I don't have scope

[Qiaozhi]

It's a pity for me because I don't have scope

It would be a good investment to get one.

[Legaucho]

Hello all

I worked last night on suggestions of Qiaozhi and to Porkluvr

Tests with the basics of Qiaozhi, gave permanent instability. Capacitor .01uF on TX ok, but the same value plus some adding on RX make the trouble.

Tests with the basics of Porkluvr, allowed to have a threshold interresting (I have one on TX .01 uF capacitor in parallel and 590pF, one .0033 uF capacitor one RX).

I confess I did not continue further because I was tired of my day.

But I have another question which has me pure novice I can not answer: What is the role of C7 and what should be its value? (see attached diagram).

I could not do testing for over a week because I must take time off.

[maxbiri]

C7 must be 10 nf or 10000pf, i presume it's a simple error on foma schematic.
First stage with c7 is a passband filter.
For coil use the 10 mH coil as receiver not TX.

Bye max

[Legaucho]

Thanks you maxbiri, I have make a big mistake , sorry for Qiaozhi and to Porkluvr

[porkluvr]

Thanks you maxbiri, I have make a big mistake , sorry for Qiaozhi and to Porkluvr

Sorry? What did you do?

You may already have figured this out but I'll say it anyway. Here is a method you could use to dial in your tx. If you have a freq meter you should first make sure that pot B can tune the 555 output to 20kHz +/- 1kHz. You will probably have a wider range than that.

An LCR meter is very helpful.

(1) Calculate the inductive reactance of your coil using 20kHz as your target frequency.

(2) Plug the value from (1) into the capacitive ractance formula determine the necessary tuning capacitor value.

(3) Double check your work using the frequency formula

Connect everything and turn it on. Connect your multimeter to TP and ground.


(4) Turn Pot B to about 50% position. Tweak pot A to obtain highest reading. If your
meter reads more than about 11V you should dial back pot B during this procedure.

(5) Turn pot B to obtain about 11V. I selected this number because with an 8V power supply you can only obtain about 16 Vp-p before your waveform starts getting distorted.

I assume that your meter reads the RMS value (but if your meter reads average value, then you should dial in 10V).

The meter you are using may not be accurate at 20kHz so it will be OK to see what
happens above and below 11V. Too much amplitude on your tx reference to the disc and geb circuits can cause trouble and you should not expect to get extra tx power without consequences. You can see why it is very desirable to have an oscilloscope because then you simply look for 20Vp-p.

I have no good plan for how to tune your receiver without an oscilloscope so that must
be done by trail and error. Actually, I am not sure I could tell you how to tune even with a scope, I would have to take an educated guess.

So far as I know the original rx circuit is un-tuned (I don't see a parallel capacitor and that 0.22 capacitor serves only to AC couple the coil to the amplifier) but if you need to insert a parallel capacitor to make a particular coil work, do so.

[amtech2005]

I read on this Forum that Tesoro has never put pcb guard rings on any of its detectors , the circuit board [trace] around the fet transistors ? Is this a critical mistake or not really a problem ? Was this problem only for "through hole designs" or it is not necessary with all the "umax series" which are surface mount ?

HH.................Eugene

[amtech2005]

Maxbiri PCB component overlay needed !!!

Hello Maxbiri !! I am using your pdf "pcb file" , do you still have the component overlay , silkscreen or x-ray [top-side] ?

This image is from your pdf file from 2008 .

Thank-You...............Eugene

[Legaucho]

I'm back Thanks porkluvr, i will try that.

[maxbiri]

Hi Eugene

i presume i never posted all documentation for my lobo design because i hadn't good result.
I haven't more design for components side, sorry.

bye Max

[amtech2005]

Hi Eugene

i presume i never posted all documentation for my lobo design because i hadn't good result.
I haven't more design for components side, sorry.

bye Max

Hello Maxbiri . This image you posted was very hard for me to see . No values given just the standard numbering order of each type.

I am starting work on my 1st homemade Lobo pcb board right now , I will post some photo's in a few hours , no laughing please !!

HH...................Eugene

[maxbiri]

I Eugene

I havn't posted all documentation about my project because i hadn't godd result so if you are starting with lobo circuit i think it's better use a different design or project.
Bye Max

[amtech2005]

I Eugene

I havn't posted all documentation about my project because i hadn't godd result so if you are starting with lobo circuit i think it's better use a different design or project.
Bye Max

Maxbiri . I read all your Lobo posts and you were very close to being successful .
Soon you will be able to modify/correct your circuit boards , if you kept them all.


I am starting the Lobo pcb right now . Picture 1 , do not use these little hobby iron's for pcb image transfer , hot enough but not enough pressing power . The handle can break with to much pressure . At least with my pressure it will !!

Picture 2 , I used a standard clothes iron set to medium wool / silk setting , it worked great for me !!

Do not use regular steel wool for anything , use scotchbrite kitchen pads . Making progress now . Used a famous PI circuit for practice and worked perfect with the big iron , so it will be next project ?
We should call this topic "Tesoro Lobo Good News" . Sorry , had to put the fuzzy pictures in pdf folders . I will change to better photo's later as I progress on my Lobo project .

1st practice bad
2nd practice excellent .

HH...........Eugene

[amtech2005]

1st Lobo transfer easy , now for the etching !!! Yup , right on schedule !!

HH.........Eugene