One of my favorite brand of metal detectors were the D-Tex. My first real detector was a Tiny-Tex back in 1969, it was a very small box BFO unit. Remember finding many coins with it around school yards and parks. My first gold ring was found with it and not to far away a Canadian Large Cent.
When the VLF/TR Discriminator SK and CK models were introduced around 1979-80, I convinced a local dealer to handle the line. When they arrived I field tested them and helped sell them. They were excellent working machines as they were based on the Garrett Master Hunter and Groundhog series. Found many deeply buried old coins and relics with them. In VLF mode they can detect very deep, comparable to makes and models made today.
OWNERS MANUALS 1980-82
SK, CK, TK, MK or RS models
Battery Tray Mod
For the models above that are slightly older, the batteries were mounted in a tray and slid into an opening on the side of the detector. If you have one of these units, you may need to do a 20 second mod.
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D-TEX Electronics, Bill Mahan (founder) has been manufacturing quality metal detectors since (1956) the early days of treasure hunting. Over the years, D-Tex has pioneered many new developments in the industry. Never ending research and development, precision parts and strictest quality control standards. D-Tex has made BFO, TR, VLF/TR and just before it closed it's doors around 1984 several motion and water hunting machines. Bill Mahan's son went on to purchase Gold Mountain brand of metal detectors and took along parts. You will see some similarity between Gold Mountain VIP and the D-Tex SK-CK models.