Top of the lieneup before the later RT-1024 monster.
5-gang dual-gate Mos-Fet FM front-end, high-selectivity ICs and ceramic filters, PLL MPX, 3-step muting threshold and FM detector output for (potential) (maybe) (shenever) 4-channel broadcasts.
The AM section uses 3-gangs, 1-stage RF stage, ICs and ceramic filters.
A nice design which Akai also went for later in the 1970s... but maybe Rotel built the Akai tuners :)
I believe this particular lineup (RT-824, RT-624, RT-324 & RT-224) to have been export-only.
The manual is still downloadable at Rotel's.