From the beginning of "modern" hi-fi : when specifications started to leap upwward but build-quality still was "old-school", ie. made to last ten lifetimes.
Also slightly after TRIO dropped its shortlived Kencraft kit adventure - the end of the really "old" world when Marantz, Telefunken or Dynaco also sold kit versions for enthusiasts with a soldering iron ability.
The KA-7300 features Dual Power-Supply : two transformers, two driver/pre-driver boards, two heatsinks, and four 10,000µF caps for true, proper, dynamic capacities and s t e r e o separation.
Also, beginning of "high-end" a 2-gang attenuator sourced from ALPS (who else ?!), DC phono and power stages, ICL inputs, FET differential input for the EQ stage and many tone-altering controls within their own NFB loop.
The input selector is remotely switched with a shaft to avoid wires running all over. The tone controls and the other controls remain however on the other side of the enclosure so some wiring still is running back and forth...
Speakers nevertheless have their own relay so that part of the path was reduced.
The power-block is, like in many Kenwoods of the time an integrated Darlington pack : a good solution to keep everything tight and thermally "made for each other" inside, but a bad solution if the packs have to be replaced 30 years after 1975...
There are two versions of the KA-7300 : the export version has an added two-step "presence" switch next to the treble turnover switch, a DIN tape i/o and a third set of 'speaker terminals.
The japanese original had none of that and was, naturally, named TRIO.
The export 7300 remained available until early 1977 in the USA.