Transistors: (NEC) ST-16B (oscillator-mixer), ST-16A x 2 (IF), ST-3C (AF driver), ST-12 x 2 (output)
Diode: (NEC) SD-46
Speaker: 3-1/2" permanent magnet
Output: 60mW (distortion free)
Power source: 6V : UM-2 (C-cells) x 4
Aiming to achieve maximum sound quality for what was then referred to as a medium size portable transistor radio, the superhet circuit included an AGC system and the radio was given a large 3-1/2" speaker. (NEC went as far as suggesting that the NT-6A was designed to fit into a pocket. I suppose it might fit into a really big coat pocket, if one forced it in there....)
NEC opted to use socketed transistors on the NT-6A, an act of precautionary overkill that can be found in the first transistor radios from several Japanese makers. Other examples include the NEC NT-7H, the Hitachi TH-669, and the Nippon Victor TS-600.
The photo below shows the ST-16B transistor in its socket. I know it looks as though the stamp reads ST-16E. But that's an illusion caused by the stamp not wrapping around the curve on the oval transistor, thereby cutting off the right edge of the "B".
And below you can see the pair of socketed ST-12 transistors as well as the ST-3C on the AF circuit board.