Sony's best portable cassette recorder, lineup-wise below the open reel portable TC-510-2 cutie.
Market-target-wise, the TC-164SD is the forerunner of the famed and much lighter TC-D5 which was launched two and a half years after the 164SD : rugged semi-pro field recorder.
The TC-164SD comes in the chronological middle of the Sony DENSUKE recorders : twenty-four years after the 1952 original and twenty-nine years before the 2005 (digital) PCM-1.
DENSUKE is a nickname forged after a Sony portable recorder was shown in a popular weekly press cartoon of the Mainichi newspaper.
The name stuck and Sony Densuke survived the original Densuke chararcter, hero of the cartoon.
Of course, in absolute Sony style, Densuke isn't written or tagged anywhere : one just has to know if a recorder is of the Densuke family or not.
Starting with the TC-D5 series, those belonging to the Densuke family always had a "D" added to their name : TCD-D3, TCD-D10 etc, where the second D is the Densuke (and the first is Digital).
The TC-4550SD was known in Japan as Densuke DD for its direct-drive motor ; it was lighter by 1/3 and smaller by 1/5 compared to the previous TC-3000SD "Densuke" (the TC-152SD outside Japan).
Of course, the TC-164SD still weighted more than 5kg and Walkmans still were two lightyears away, but its long lifespan indicates that it must have been worthwhile.
The TC-164SD and TC-D5, sales-wise, blew all the competition's best efforts : Technics RS-686DS, RS-646DS, JVC KD-2, KD-4, KD-1636 MKII...
Sound-wise, the D5 still does.
Even famed Nakamichi (with the 550) or Teac (PC-10) couldn't compete with Sony on this side and... Uher on the other.
The EL-D8 portable ELCASET should have played the role of Attila... but didn't.
Can't win all the time.