Neither an ESPRIT unit, nor a pre-Esprit, the TA-N9 monoblock was sort of "in between" : alongwith the prototyped but sadly unproduced EL-D9 professional Elcaset deck, the PS-X9 masterpiece, the PUA-9 long tonearm and the APM-9 which was finally produced as APM-8.
Enclosed in this monster was all that was meant when the PPS/PLPS system was introduced by Sony in 1977 : huge power in small and lightweight boxes. The Heat-Pipe and MOS-Fet were later novelties but the N9 wasn't particularily small or easy to carry around :)
Heat-Pipes were en vogue between 1978 and the early 1980s ; Luxman carried the feature as late as 1994 (!) and the last versions of the L-570. It seems the Freon gas held inside was at some point deemed dangerous, which is why seemingly all manufacturers (but Luxman) stopped putting Heat-Pipes in their (hot) amplifiers...
Not counting the EL-D9, the TA-N9 is the most elusive of all "9" units ; the highest serial numbers spotted are #253 and #289 but there were about two dozen pre-prod samples made as well. So I guess some 300 were made (= 150 pairs).
There must be very few surviving units and those that resurface in Japan are almost always the pre-prod. samples...
Each N9 was delivered with urethane-coated Litz connecting wires nevertheless - a staple of high-end Sony since 1976.