VCO Mod with 18'' Mono Help

Hi Ismael and all.
Ismael has recently completed the vco & gpm mod to my SD2000.
Im more than impressed, Can anyone help me here with advice I was using a coiltek dd and a current gold stalker mono with pleasing results. So i thought id give the original 18'' ML garbage bin lid mono a try the old f/glass version on firing up the vco the detector balanced perfectly on ch1 but when switched to ch2
there was not any change from the pot nothing just a constant non flucuating hum
this was done on the field btw. Ok i blamed the connection and re checked everything but same result thinking perhaps id fried something as I was running 8+V I fitted the dd and all was good again. The 18'' was brand new when the 2000 was current and has never been used or damaged any suggestions appreciated.
I did email you Ismael on this but Im assuming you are away or there Is an email problem.
Happy Hunting to all.
Regards BuckAu

Hi Buckau,
Where was the gain set for ch2? If it is set too high it can cause the amplifier to overload and shut down, causing the stable unresponsive threshold. When I set the gain on mine, I start from min, and increase it until it overloads, and then turn it back about 20 or 30 degrees.
What frequency settings did you try?
Did you try turning the voltage back?
Cheers

Thanks Mechanic for reply,
The GPM gain on both ch1 & 2 were fully off the only freq i tried was the vco. I thought after I should have re tested on the fixed channells 1-2-3 but I neglected to do so also I thought of changing V but my Li-ion pack Is not reducable and I didnt have my 6v gc with me.
Weather permitting I will re test tommorow with the above. Mechanic what freq do you find to be otimum.
Kind Regards BuckAu

Hi Buckau,

I like to use a high frequency 3.745 mhz, or something around that range. It is really good for the smaller bits. However it all depends on the area that you detect at, if the nuggets are deep big ones(I wish!) use a low frequency with a big coil. If you are looking for the smaller bits use a higher frequency. The only problem with the higher frequencies is the earth balance gets upset, although I don't know Ismael may have a fix for that.

A good test for you to do would be get some different sized targets and try them on different frequencies, and also with different coils to get a feel for your machine.

It is possible that your 18" mono might be no good. The capacitance may be too high, there could be a bad connection in the plug. Try using it on a low frequency.

Cheers

I have been trying to get reacquainted with my modified 2000 since parting with a 3000 hoping that now with a VCO fitted and able to wind down to a lower frequency than the original fixed 2 meg Xtal it may hit on the deep big ones or as mechanic says ”I wish”.

My coil of choice for the job is a NF18”mono although no idea if its Q is near to the original concave fiberglass 18” mono as I have read the SD works best using a coil with a Q 4.2 - 4.5. I do still have my 2000’s original concave 18" mono and since my SD2 is one of the first Series (s.n.023073) I expect it’s 18” mono (s.n.0283) is also one of the first produced. I have no idea how many different concave 18” monos were produced although there does seem to be different colours of green used as was the case with different types of backpacks and their colours.

I read Woody says good shielding is what makes a good coil and I expect not much was used in those early concave monos as well securing windings against shock not being a priority. However some of my early testing with my old 18” concave mono gave impressive air results with large targets waved above.

I agree with mechanic to do testing and I sure have a swag of test results with many different coils and targets. My favourite target for tests both in-ground and air is Doug’s Aluminium block which I believe has a decay response similar to a 12-15oz nugget.

I have noted since operating my modded 2000 even with good aftermarket coils a bump to the coil seems to cause the detector to jump a gear or into another frequency although if I bump the coil again it settles down. Maybe a coil connector or power connector problem at the control box but I have them nice and tight and secured so not sure what could be happening as other bumps cause nothing to happen at all. I suppose just something to get use too by operating a dinosaur of a machine.

Mechanic have you settled on a preference for a low frequency?

Gary

Hi Gary,

2mhz is the lowest frequency I have on my detector at this point in time, as I have not completely finished my vco(slack! and easily side-tracked) I need to make a new circuit layout and build the final board, and build another end plate, as I don't want to butcher the original one and I can put all the knobs closer together!

That being said, the other week I found a piece of 1/1/2" angle iron at about 2 foot with the 11"DD in 3.745Mhz. Both ch1 and 2 picked it up. I wanted to walk away several times, but I could see the headlines "Man finds nugget bigger than hand of faith in half dug hole"

Cheers

Thanks mechanic and interesting you say the 3.745 freq went that deep with the 11"DD as I have played with a few freq. settings with the VCO on large targets and blowed me down the fixed Xtal in pos.4 at 3 meg gave me a high signal response in air on large targets with my NF 18"mono. Although this Xtal is not as high as your 3.7 meg it was sure a surprise since it matched a low freq. setting with the VCO.

Would it be a different story in-ground I can not say at this stage.

Gary

The signal was very faint and wide. If it had not been on both channels, I would have written it off as ground noise.
Cheers

Hi all my VCO runs from 990 Kc to 4.5 MHz but I find the best frequency here in S.A is 2.8 MHz it seems good on all targets so good I run my 3500 at the same freqency. my VCO is a modified version of Ismaels design with its own voltage regulation so it can be used as a plug in out board unit if need be, I have done all the mods myself with help from Ismael and others my main bent is building coils. Regards Ian:)

Hi Guys just some observastions I went to some very hot ground near Ararat yesterday. I say hot because Ive seen a lot of late machines behave way weird here with monos.I did not attempt to run a mono Instead a 12'' dd coiltek.
With the gpm turned off. I could ground balance ok but with any gain it would be so unstable I doubt you would persist.
no matter what i did I ran out of gb on ch 2 evenwith the xtra pot i could not tame the gb. In frustration I turned the gains fully down vco till smooth ch2 and vco to 2.8Mhz (fully ccw) 8.4V and the machine ran very very smooth only mis behaving if coil struck a rock or branch.
After a short time I heard a very faint but precise target the one that excites you after 65mins digging the thoughts of Mechanics post ringing in my ears quote= Man finds nugget larger than hand of faith in half dug hole.I couldnt find the bloody thing and I was that deep that my pick wouldnt reach the bottom of the hole. I did the track back to my ute and grabbed my trusted vlf with 6'' coil and pinpointed the target i was just off to one side but a good 76cm deep. My optimisum turnt to dissapointment when the whites MXT vlf gave me the Iron grunt and probabilty of 60 percent iron sure enough a peice of horse shoe from another era. However point in fact it was bloody deep and this ground has seen a lot of coils and combinations. Perhaps the more learned distinguished the target as bad but to me it was mellow and good sound.Sorry if im rambling just wondering anyone had similar experiance's with the Modded 2000.
Happy Hunting to all.
Regards BuckAu