Like a few other Luxman units from the times, the K-05 isn't was planned in the first place : it was to be the small one !
However, the X-3K, the really very big one, sadly never went into production.
The GT Transport (not related to Yamaha's contemporary "Gigantic & Tremendous" tag), is the star of the show while the CTS was getting to be more common within other high-end tape decks... But the combined results made for quite a machine.
GT is a zinc-alloy diecast drive which includes two pairs of capstan bearings for perfect and forever perfect geometry of the closed-loop dual-capstan and 3-DD motor mechanism.
The heads are µ-aligned and 3-layer lamination (rec), HIP ferrite (Hip Isostatic Press) with special contouring (play) and sendust/ferrite wih assymetrical dual-gap (erase).
CTS is an automatic calibration system which sets bias, level and eq separately then correlatively to match the optimum points for all. A supplementary manual bias calibration pot allows the user to match his own optimum point.
The Dolby ICs were sourced from Hitachi and the inside hides an ALPS 4-way DIP switch to select high-frequency attenuation !
Duo-ß and DC configuration makes the audio circuits, with magnetic materials avoided. OFC wiring is used between the heads and the amps and the chassis is copper-plated ; power-supplies for each section are regulated.
Almost previsibly, the Luxman K-05 is an Alpine AL-90 in disguise !
The first hundred K-05s produced used an unmodded Alpine mechanism, the later ones had some mods performed but still, K-05 = AL-90.
Luxman's CTS system was originally named BLES on the AL-90 - whatever the marketing tag, CTS = BLES.
The display and layout of the electronic functions' panel are the same as on the AL-90. In fact... everything is the same.
If the X-3K had been produced, it would've been a Nakamichi DRAGON and Sony TC-K777ES killer, no doubt !
And an AL-90 killer, too.
Many many nudies of the heads (replacement), boards, VU, motor here.