I do not have mt7601u in /lib/firmware although there is a lot of other stuff in that folder, which presumably came from the fdrv at bootup.
IPDATE The dilatory LxPupXenial16.08 installation, which has a 4.x kernel had acquired a mt7601u.bin in its /lib/firmware, presumably from the appropriate pet supplied. I copied that to the k4.12 (this one) and it is now running off the wireless usb. My thanks to everyone who helped.