Tesoro Silver uMax Ground Balance

[Delano1981]

Hello everyone,

I have a Tesoro Silver uMax detector that I want to add ground balance to. I have searched all these forums, and can only find references to past posts detailing the modification, but I can't find the original posts. I gather from what I have read that there is a trim pot for GB (at least on other models) located near the middle of the circuit board. You remove it and wire a potentiometer in its place. I opened the control box and there is a trim pot about in the middle of the board. Can any of you help describe this mod in more detail? What is a good potentiometer to use, and after the mod, does the ground balance affect both the all metal and discrim. modes? Do you adjust GB like the other models that include GB with a tone that you can hear as you lower the coil, and is it done like the other models in all metal mode? I guess what I mean is that after the mod are you able to hear a tone as you lower the coil towards the ground?

Thanks

[porkluvr]

I don't think that anybody here has R.E.'d the Silver uMAX. The phase network may be like one or another version of Silver Sabre, but if so, which one? There are several very different versions. Look at the two schematics I posted.

The SSII uses a scheme similar to the Bandito, and the two controls are not interactive. The Silver Sabre Plus uses a phase network scheme where the GEB control affects the DISC phase, but that may be OK. To be on the safe side I would suggest that you try to R.E. the phase portion of your detector and match it up with either the SSII or SS+. If it's like the SS+, think twice about messing with it. If you decide to modify, to cover yourself - measure the pot that you remove so you know where to set it in case you want to change it back. Or use a scope and compare GEB phase against the oscillator.

I have a (SMD) Silver Sabre II (it says so, anyway) that is different from the posted schematic, but its phase network looks similar. I Just modified it, but haven't figured out how to ground balance. I need to go back in and add a 1k resistor to ground, so I don't have squacks at 100% rotation. I want to scope it to gain a perspective of how everything works but I'll have to use a scope at the local community college.

My cabinet is small (maybe just like yours?) and I had to move the DISC pot down, so I could fit the larger GEB pot up top. I did not plan for that, I first tried to cram the new pot at the bottom. No such luck.

You should probably use a 100k 3T or 5T. I acquired some 125k, 5T pots from Surplus Sales of Nebraska. If we use a value that it too, too high, then ground balance adjustment will be touchy. I can parallel a fixed resistor to lower the overall resistance, if the adjustment seems too sensitive.
http://www.surplussales.com/Potentio...ltiTurn-3.html

Get the H755T. I started with the 510-14A, but one of the terminals was open by the time I got done soldering, and the action is not smooth.
You should have a fixed 1k resistor in the circuit. Add one if one's not already there.

You had some questions that I don't know the answer to. You'll be a pioneer if you want to. That's all I can tell you so far. Good luck with it, and, don't rush.

[porkluvr]

To set ground balance, you would want to read and follow the GEB setup procedure for one of the manual GEB Tesoro models. The Bandito, for instance.

Here's a snag I've encountered, but you won't: the threshold adjustment on the Bandito (and Silver uMAX) is a front panel pot, however on my GSII the threshold is only a trim-pot with a little knub sticking out the back; not made for frequent fiddling. So, how am I going to ground balance with only a little knub to adjust the threshold? Whoops. I wish I had thought about that before. It will difficult to setup unless I replace the threshold trimpot.

Well, shucks. I have a 10V Bandito hybrid in work, made for a Bounty Hunter Quickdraw cabinet. I will see if I can fit another pot on my micro SSII front panel, but I am thinking about attempting to transform the micro SSII into a GoldBug. Hmmm, remove the speaker, I'll need a coil.... .

[jonas63]

This is for a Cibola....but should be the same with a Silver Umax

http://www.jb-ms.com/Carlsforum/Aug2...185585128.html

You can buy the 10 turn pot here:

http://www.rapidonline.com/productin...moduleno=29588

[jonas63]

Another Cibola ground balence mod, it´s in German, but Google translation came into rescue :-)

http://translate.google.com/translat...&hl=en&ie=UTF8