I've been using Tesoro machines since the beginning and I think I understand them.
Tesoro detectors have from day one been mostly no-nonsense detectors. Some would argue that the DeLeon and Cortes are departures from this philosophy but I won't go there.
But the Vaquero and Eldorado (and others like the Bandido 2 uMax, Tejon, etc.) are definitely no-nonsense, maximum results, machines.
You get maximum depth and sensitivity via complete control of that which produces these results--mainly, the sensitivity and ground balance knobs.
Tesoros are basically 1980/90's technology. That's not all bad. During the 1980's to early 90's most of what really works in coin/ring hunting was developed. Since then the "new advanced technologies" are highly questionable as to their real worth (to put it mildly).
But all Tesoros (and most other brands) suffer from one serious problem. That problem is the tendency for the coil to not be perfectly matched to the detector electronics. The coil is the detector's antenna. The electronics is basically a combination transmitter and receiver (plus lots of added features). All transmitters must have a perfectly matched antenna in order to function to maximum potential.
The problem with Tesoros is there is no way FOR THE USER to manually keep the coil (antenna) tuned to the electronics. SOMETIMES this coil/electronics miss-match is what is behind statements like "my Eldorado gets 2 inches less than my Vaquero on a quarter."
The coil/electronics adjustment must be made by some knowledgeable person (it's an internal job).
Every year Tesoro lays out big bucks in labor and shipping costs because loads of people return their machines due to "poor depth." When they get their detectors back they usually say something like "WOW! it now gets 2-3 inch more depth!" Many times the reason being many are out of what the company calls "calibration." For factory preset detectors like the Silver uMax it's both coil/electronics balance plus ground balance.
The so-called "hot detectors" are simply detectors with near perfect matched coils. Some coils are not right from the factory and can never get great depth no matter how many times they're calibrated.
The most difficult part to make on a VLF is the coil. It's difficult in the sense that it must be absolutely precise. This precisness is needed due to micro mini power. We could say a detector is only as good as its coil.
This is one reason I love the Tesoro uMax 12x10 concentric coil. I've never gotten one that was "cold."
I just sent my Bandido in for a knob fix and with that the company highly recommended a "calibration." When she comes back she'll kick butt again for a long time. That is assuming I don't leave her in a mega hot car trunk for several days or drop her from the second floor window
To date the only company to address the coil/electronics issue is Nautilus. All others have considered it too much for the average user.
So, getting poor depth? Maybe it's time for a "calibration?"
