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@bluesky, I too think that the AU-717 could be put forth as the idealized representation of Sansui's design and engineering expertise. Not only for its sound quality, which sits more or less at the mid-point of their evolution (and refinement) between tube amps and the late stage Alphas, but also in terms of their design aesthetics. There is no doubt the AU-717 (and related models) were a revolutionary moment in the look of home hi-fi, and it was a design knocked off endlessly by others for many years hence.
The matte black, asymmetrical panel layout with oversized volume control, flush pinpoint red LED indicators, and sensibly placed controls for all other key functions, along with the simplicity of text rendered in white Helvetica, was a stroke of genius for it's time. Probably the only other "look" that had that much staying power and consistency was that which Marantz used for nearly the entirety of their "golden era". I suppose Yamaha gets a nod for their signature look in the 70's as well, as they also remained remarkably consistent for most of the decade, across their entire product line.
Really, the AU-717 is an amp with a sound that can still satisfy the discerning listener today, still looks great, and was still built quite well, even if Sansui's peak build quality could arguably be placed around 1970-72, before Yen valuations began dictating cost reductions. I consider it probably the best all around example of Sansui's excellence at nearly the highest point of their existence.
And it bears pointing out that the 717 line up was a mainstream, attainable product. The late Alphas, excellent as they are, were inarguably esoteric, niche products of very limited distribution. I don't think Sansui ever achieved more exposure or market share than they did around the time the 717 was in production.