I took the Pioneer RT-707 to Anders for service and adjustments and borrowed this Akai to test (and write a short review of here).
It is an Akai GX-4000D from the 70s. I put in one of my reference RTR recordings of Dave Brubeck to see how it sounded, but could not figure out how to adjust the speed. It sounded good, but slow. I kept pressing what I thought was the speed button, thinking it was malfunctioning. After scratching my head for a while, I downloaded the manual from hifiengine and figured out that the speed is determined by the size of the capstan pulley. An adapter is stored behind the tape head cover - alas in this one the adapter is nowhere to be found (it is probably at the store). The button I was pressing only changes the eq (not very intuitive, Akai engineers). With the adapter unavailable I moved on to recording a test tape at the slower speed. I spun Winston Marsalis' Black Codes and let the machine do its thing at 3-3/4 ips. I played back the tape and it sounded… ok - not great but not bad - definitely better than any inexpensive cassette tape deck. I then cleaned the heads (went through two cue tips) and demagnetized, and things improved significantly.
Note that this is a very bare bones deck, no autoreverse and you can probably have two beers while it slowly rewinds a full tape - but it does the audio job well. It has an "SOS" button that I then decided to test to see what it did (never mind the instruction manual - which I ignored), thinking it added some form of noise reduction. It doesn't. It stands for Sound On Sound, so I guess it shuts down current to the erase heads so you can do sound overlays. The same stuff we do so easily today in Garageband or Audacity was actually a pain back then (thank you computers). So that recording ended up a blurry mix of Winston Marsalis and the next record I spun, some steel band from the 60s.
My overall impression is that this is a great RTR (specially if you have the adapter and can record at he higher speed for additional fidelity). The controls are the opposite of "soft touch" - but in exchange it feels more reliable - a deck you can count on when you want to watch reels turning.
Here are some pictures: