One of the most remembered and sought-after reel-to-reel recorder although, arguably, not the "best" - we could name the Technics RS-1500U series or the Sony TC-880-2 to name but two masterpieces.
But what lavish looks the 646 was graced with !
And it sold extremely well, too.
And it was updated to become the famous GX-747 and GX-747dbx.
But it couldn't spin at 38cm/s...
Until the japanese catalog I have is translated from japanese to english, you can read more about the GX-646 at Frank Oomen's website.