Before treatment… and after!
Once upon a time, Sansui was a mere transformer manufacturer. It was natural progress that Sansui started manufacturing amplifiers and tuners in its early history. In the late 1950’s to the early 1960’s, Sansui had developed a sense of mission to be a world class audiophile manufacture. That was the reason that Sansui introduced the first pre-main (integrated) tube amplifier SM-88 in Japan. Sansui introduced only two more tube integrated amplifiers, AU-70 and AU-111, before they moved forward to the solid state silicon transistor amplifier, AU-777 in 1967.
From 1967 to 1970, Sansui introduced the array of the single number three digits integrated amplifiers. They were AU-222, AU-333, AU-555, AU-666, AU-777, AU-888, and AU-999 followed by improved versions; AU-555A and AU-777D. The sound of this series was very close to that of tube amps. Even mixing with tube amplifiers with frequency divided multi-power amps system, it sounded natural.