The last pre-Esprit unit to appear.
If the looks are radically different, there is a fair amount of parts sharing between the TC-K80, TC-K96R, TC-K60 or the later TC-FX1010 and the K88B, but the latter really was the higher-end of Sony's '78/80 cassette recorders.
Most visible at first is what makes the K88B almost invisible : the Power Loading Module.
Despite the somewhat overblown name, Sony didn't do this the gimmicky way with a cheap-but-complex arrangement of belts and gears but with a straight hardware system : one motor rotating a big endless screw moves the entire drawer/drive/display assembly, the latter sliding on extruded aluminium rails.
Mechanically simple, frightfully reliable and silent as can be - very elegant.
Most visible also are the LCD meters which Sony already used in 1977's TC-K8B (its largest incarnation) and would be carried on into the professional successors of the PCM-1 (PCM-10 and PCM-100), the extra-rare MX-7000 mixing console as well as in some Sanyo and and Alpine units.
These LCD meters are far more readable than regular VUs or FLs but they do take a fair spot inside to hold the three PCBs, discharge neon and window box plus a log amplifier board, a full-wave rectifier and d/a converter.
Which is probably why Sony's LCD meters weren't used beyond 1980 : too pricey, too big.
The rest is as high-end as can be, for an upper-mid class K7 recorder :
feather-touch keys, S&F heads (for Metal tape compatibility - F&F can't take the needed flux density), four-gap erase head, Sony-built Dolby ICs, three direct-drive BSL motors with Quartz Lock, Magnedisc imprint / reading head, DC rec/play amplifiers and big 2x 2-gang input level pots.
Also two transformers (one for the five regulated power supplies and another for the sole LCD meter), a substantial back heatsink, all steel, metal and extruded aluminium and a typically Sony finish quality, ie. unmatched by anyone.
Features-wise, it's all there in a modern way : AMS search with memory & program, cue mode, digital counter, bias & eq switches, switchable MPX filter etc.
Japanese versions (TC-K88, silver color) had a rec/play timer position added to the power switch (the original vintage knob ;-) which worldwide units didn't have. We obviously weren't deemed advanced enough to use a timer !
However, as Sony really was Sony, the K88B was launched with two different lineup tags : the almost old ESPRIT (1978) and the "new" ES !
The latter began being attached on components only two years later (even if the ES series was as old as 1965), while the former only was there as reminder of a corporate division setup exclusively for a series... to which the K88 didn't belong.
Neither tags are witten anywhere on the K88B itself either : Sony is Sony is Sony is Sony.
Also, despite its high-end pretensions and actual quality, the TC-K88B only is a two-head recorder - no tape/source monitoring possible.
This confusion didn't bother anyone, obviously for the K88B was very well received in Japan and elsewhere and sold very well - Luxman's president didn't use a 5K50 at home but a K88.
I for one own a near new TC-K88B with an RM-50 remote : educated hi-fi at its best.