Oddball DC-xxx tape drive

I've got a DC-300-footprint tape drive in my collection of peripherals, circa 1986 (chip dates) for which I'm trying to identify the medium. A DC-300/600 cart fits perfectly and is spun a bit by the drive before the error light comes on. Upon close examination of the drive internals, the surprise is that it doesn't use an optical sensor to determine BOT/EOT, but rather contacts on either side of the read/write head that apparently make contact with a conductive metallic strip on the tape. So the medium isn't DC300, anyone know what it is? The interface is a 50-conductor one, with unit selects from 0-3, but it doesn't seem to be QIC-02 or QIC-36--and it's not SCSI either. The drive has a motherboard with two cards in it--one appears to contain the read/write amplifiers, the other contains a 6803, 6522 and a 6821 and a 2716 EPROM with a 3M copyright sticker. The manufacturer is ADIC, but I'm unable to come up with any documentation on the web for this beast. Cheers, Chuck