Sorry to hear that because it means you missed out on a lot of fun, a lot of good targets in impressive quantities, and also missed out on some education and learning about metal detectors, metal detecting, and what we gave up in performance to get to where we are today.
I was fortunate to get an early start in having fun. Garrett Electronics, later Garrett Metal Detectors, started their business in 1964. In early March of 1965 I built my first Metal / Mineral Locator and have stayed very active and involved in this great sport since the start of is popularity. And along with a number of other brands back then, by the latter '60s I was enjoying some of those early Garrett devices, and went quite heavy and committed to Garrett products from '71 for the next dozen years.
I have hunted many of the types of places you'll see in all of those Vintage Videos, including quite a few out-of-the-way places in Utah (where I'm from) as well as ghost towns, stage stops, old resort sites and picnic groves, Dance Hall sites, mining encampments and townsites mainly in Utah, Wyoming, Colorado, Idaho, Oregon and Nevada. I kept at it as long as my health and mobility allowed me to. most of the more rugged places where it called for hiking in I did from '71 to '90. when I still could.
Well, it's class time:
Today we see a lot of detectors that have a control labeled 'Threshold.' Technically and historically, that knob/function was properly called a 'Tuner' control. "Threshold" isn't a name of a control, it is a reference to a proper audio setting you achieve using the 'Tuner' control. You adjusted the 'Tuner' just to the point you could hear a proper slight audio Hum or 'Threshold' level.
The 'Tuner' on a Transmit / Receive detector, aka Induction / Balance, would let you adjust to hear a functional slight 'Threshold' hum. On the earliest TR models, you would manually 'tune' for a working Threshold' level, and then position the search coils a uniform distance from the ground. Let's call it a 2" height just as an example. You had to maintain a uniform coil-to-ground height in order to keep a stable 'Threshold' hum.
If you lowered the coil towards the ground, let's say to 1", it would then have a greater amount of ground mineral impacting the EMF and the 'Threshold' would drop off a bit or usually completely null out. Depth and general performance would suffer. If you lifted the coil away from the ground, such as up to a 5" height, it would be farther from the ground mineral and therefore the ground would have less effect on the EMF and that would result in the 'Threshold' level increasing abruptly and get too loud for the detector to function properly.
So with those earlier TR models it was important to adjust the 'Tuner' for a proper 'Threshold' hum at the operating level, and maintain that. The user would have to keep a proper coil-to-ground relationship and, when necessary, re-adjust the 'Tuner' control to establish a functional 'Threshold' hum.
Design engineers soon incorporated an "auto-retune' control or in-circuit auto-tune to help maintain a working 'Threshold' when there was a change in coil height or in ground mineral make-up. Using any of the TR-Discrimination models also caused a problem because the more the operator increased the Disc. level away from 'ground' or 'iron' conductivity level and up to reject lower-conductive foil or higher to get rid of pull-tabs, the conventional TR mode would be even more reactive with even a slighter coil-height variance.
Thus, in those earlier days of TR detectors, most operating at or close to 100 kHz, it was the ground mineral environment that was our biggest struggle to deal with. We didn't have as much trash, or nearly as much higher-conductive trash like we have today or for the past 30+ years.
George Payne is credited with engineering the first ground-cancelling metal detector for the hobby market when he was an engineer at White's Electronics, and they brought us our first detector model that featured controls to cancel or eliminate the falsing when the coil was raised or lowered from the ground. That was patented, I believe, in '74 and the first model, the Coinmaster V Supreme came out in '74 or 75. It did not have a TR-Discriminate mode and could only be tuned to eliminate / cancel / ignore / balance-out the ground mineral effects.
It has two knobs to achieve that: A 'Tuner' control to adjust for a proper 'Threshold' audio; and another knob control called the 'Terranean Attenuator' of all things. Many Dealers couldn't even pronounce it! Today that control is usually called a Ground Adjust control or a Ground Balance control.
You had to adjust the 'Tuner 'then lower the coil and adjust the 'Terranean Attenuator', then raise the coil off the ground and tweak the 'Tuner' for a Threshold and then lower it and adjust the 'T-A' for a Threshold hum and go back-and-forth until the coil could be raised and lowered w/o any falsing.
Today we have auto-retune circuitry working so w only need to adjust the 'GB' control once we have a functional 'Threshold' level setting.
By the latter '70s we had 2-Mode detectors. One mode was the 'VLF' or Ground balanced mode to ignore the ground mineral and respond to any ferrous or non-ferrous tarage4t. We call that an All Metal mode. It allowed us to search any ar4ea, as you saw in the old videos, with the search coil off the ground and going over rocks and stumps and dirt and weeds, etc. Then, when a target was located and we could switch to the 2nd search mode, and that was the 'conventional' TR-Disc. mode.
Then we had Discrimination capability, but we were back to needing to maintain a uniform coil-to-ground relationship so as not to lose the 'Threshold' level we had 'tuned' for.
Fast-forward to today and recent years, and we have some models that lack a true, Threshold-based All Metal mode. we have quite a few detectors that have a selectable mode that is labeled "All Metal" but it isn't a conventional 'mode' but is simply a motion-based Discriminate mode at about a 'Zero-Disc.' setting and can respond to both Ferrous and Non-Ferrous targets. A few of those let us adjust to hear what they call a 'Threshold' hum, but it isn't a conventional All Metal mode, just a motion-based Disc. mode with a Threshold audio reference.
Well, did I leave anyone lost and confused? Sorry. If you ever get 'Out West' to hunt some very iron infested ghost towns, look me up. Come sit and chat for a day or two and get some hands-on experience with a few of those old-time detectors. I have some on-hand for my seminars.
More questions? E-mail me and we'll not clutter the forums.
Monte
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