dbx type II noise reduction is just that, besides preserving more of the source dynamic range than Dolby NR, it also lowers the noise floor substantially (10db iirc). You don’t need to have in-built dbx circuitry on any tape deck to benefit from it though - an external dbx model 224 or similar will give you all the benefits without replacing the tape deck. A bonus is being able to use the dbx NR unit with any of your R2R or cassette, or even 8-track tape decks for that matter.
Akai 747 w/DBX question
Hopefully there are still some reel to reel folks out there. So I currently have the 747 w/out DBX, and I have an opportunity to pick up the DBX version from a local person who owns a rather hi end audio store here in town. My question is: Is the Dynamic range extension worth the extra coin over the non DBX version? I don't record music from CD's to tape, and the added DBX if it works well should do wonders for recording from vinyl. I have owned reel to reels all my life but never this piece. Just curious if its worth the effort, and if you think it will it be an improvement.