High-end DC intergated amp with ruler-flat frequency response up to 100Khz... but which looks like a nuts'n'bolts steel block.
High-end because, inside, there is a PLPS - lots of power in a 12kg lightweight enclosure !
The F6B is by necessity partly related to the pre-Esprit TA-N86B (same timeframe) and naturally to the lineup that replaced it (TA-F80 / F70 / F60) but was quite affordable (unlike the former) and built in 1970s fashion (unlike the latter).
High-end because the attenuator is a 4-gang ALPS, high-end because of the SEPP-OCL, LEC transistors and dual-FET circuits.
High-end, too, because the TA-F6B was, alongwith the TA-F5 and TA-F4, the very first audio unit released with a Pulse Locked Power Supply.
Extremely successful in Europe, not as much elsewhere, the TA-F6B was only available in "B" colouring, even in Japan : no TA-F6 (ie. silver in colour) was ever produced.
However, pre-production samples all had a neutral grey color.
It should be noted that the nudie image below either shows a pre-production sample or a special japanese version : the european version has two more and much bigger caps on the power board (left of the PLPS box) and also caps behind the source selector - among other differences...
Nudies of a european TA-F6B, here ; a minty TA-F6B, here.