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Techna (BH) TR6
A peek inside
I got a request from a retired gentleman to have a look at this detector which he had bought for his daughter some years ago. It needed the controls cleaned and the cable had been torn from the coil. Since I had it open, I took a few pics and copied the manual.
This is a very ancient design, going back to pre-Bounty Hunter days at First Texas. Though it's of more recent manufacture, probably built in China, it's still a very basic TR Transmit/Receive circuit that dates to the early 1980's. It uses one proprietary IC that contains the bulk of the circuit, with two transistors for the audio, and only a few other parts needed. It has the older non-interchangeable 7" coil. It will detect four or five inches in depth and small iron can be nulled to an extent, but this is overall a simple machine with minimal capability.
Techna TR6 Detector
Read the manual that came with it, scans are below if yours didn't have the manual. The following are my impressions of it and some basic settings and tips.
Set Tuner knob midway, pointing up. Exact position is not critical.
Turn on Power and advance the Balance knob till the lights just begin to glow and the meter needle moves from rest to about the 1 point or a little higher. Around this setting you should also hear a slight sound.
If you now adjust the Tuner, you'll notice it alters the tone. One knob affects the other. The idea is to set it for a slight audible tone, so that any metal brought near the coil will be most easily heard by an increase in this tone, no matter how subtle. Also watch the needle for slight movements as the coil approaches metal.
Now we can test the detector. To do this, scan the ground with the coil nearly touching the surface. For now, you are looking for a patch with no signals, meaning there is no metal nearby.
If the detector sounds off everywhere you point the coil, reduce the Balance control till it barely sounds. Once you have it adjusted, find the clear patch of ground that has no buried signals. Go ahead and dig any signal you might happen to find, it's good practice.
Once you have located a clear spot or created one by digging out the junk, toss down a test object and scan it with the coil. Test several coins, one at a time. For trash, use rusty nails, pop caps, cans or whatever trash you may find. Or try a coin and a trash item together, like a nail near a dime.
By adjusting the tuner, you are supposed to be able to reject trash and still pick up coins. Anytime you adjust the Tuner, you must also readjust the Balance to get the weak tone back. If you get it set to reject trash, make sure to test again with a nickel to make sure that coins have not also been discriminated out. Nickels always disappear first as discrimination is increased.
I didn't notice the Tuner having much affect. Small iron, like a rusty square nail, made the detector go quiet and the meter needle swung to the left. So small iron is always discriminated to an extent. Larger iron, like an old harness buckle, or common coins, always had a strong response; the sound got louder and the needle swung to the right.
The detector is most sensitive when there is a slight tone coming from the speaker. This point where a tiny sound is first heard is called the "Threshold." You can hunt with the detector set just below this point so it is quiet until you scan some metal, but doing so may cause you to miss tiny or deeper targets. Experience will be your best guide. Once you find an actual target, experiment with the settings a bit, then dig it up. You'll learn a lot about your detector this way.
Battery life will be shorter when hunting with a higher threshold of sound. If your batteries go weak while hunting, try swapping them. One battery powers the audio and it will weaken faster than the other, swapping the batteries, like rotating your car's tires, will help even out their useful life.
This is a "Slow Scan" detector. You will get a much stronger response by sweeping the coil at a snail's pace. Sweep quickly, and the target may not even register. Experiment with the detector in your test patch, try to find a sweep speed and technique that registers the strongest response to a coin, relic or jewelry item. Listen for any subtle variations in the sound, there may not be much audible change to your ears until you become very familiar with the detector's sounds and settings.
If it's too cold to test outside, you may conduct your experiments by placing the detector on top of a box. Hold the target in your hand and sweep it past the coil. Remove any watch or rings from the hand you use to sweep with. You may also place the target on the box and sweep the coil as you would while hunting. If you happen to have a metal-free floor, go ahead and test there. Expect to find nails, rebar, wiring, ductwork and other metal, though. That's why I suggest using a box to elevate things away from any metal in the floor or nearby.
If you're connected to the internet, search for metal detector forum or treasure and you will find a wealth of info and lots of interesting reading.
This detector appears to have the same coil, stem and handle as used on my 1985 First Texas Treasure Tracker DX-8500. The DX-8500 was also a T/R design, but it is actually more advanced than the TR6 shown here, since the DX-8500 has ground balance, sensitivity, volume and discriminate controls. The "balance" control on the TR6 is more to balance the circuitry than for adjusting response to mineralized soils. Using the two controls of the TR6, a rudimentary null or slight threshold tone could be established that included some ground response, but target response would suffer in poor ground.
Here's the view you get when the case is opened. I added a small trimmer control to the loudspeaker, since it did not have an adjustable volume and was quite loud when sounding on most any target it could detect.
The circuit board has been flipped over to show the components. I did not mess with the internal trimmers, as that generally leads to nowhere and the controls must be reset to a more-or-less original position or the detector won't be stable in varying soil conditions, such as in overly wet soils.
TR6 Manual outside
TR6 Manual inside
The manual was printed on both sides of a standard sheet, then folded in half to make 4 pages. It reads about the same no matter which page you start with. I confess to fixing a line of type lost to a fold in the page.
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