The M series (ca. 1960-1973)
The Akai M-series consists of various models. Except for the M-11D, they all have a built in main amplifier and until the M-8 model they worked on tubes. Most of these models are pretty old. As far as I know the oldest M-model dates from about 1960. The last in line was the M-11/D, a stranger in this series since its mechanical technique is way different. The M-9 is the first transistorized model from the M-series and the first one with built-in reel retainers.
The M-10 is the only 3 motor model from this series. The newer M-11/D has only one motor. Only the M-10 and M-11 have an auto-reverse capability.
Since the older M-sets are pretty difficult to find and since I don't have any information about those sets, I will only show some of their pictures which I have been collecting during the last couple of years. You will notice they all have the two knob tape operation system. The tape guide mechanism, the location of the flywheel, pinch roller and pause knob was also "standardized".
M-9 (ca. 1967-1969)
Just like most of the others, the M-9 has only one motor but four speeds. A capstan speed change sleeve is included to obtain the higher speeds. It has a 4-digit counter, an auto stop/shut off switch, a bass filter and a double headphones output. The main amplifier has 20W output per channel.
M-10 (ca. 1969-1971)
The M-10 has 3 motors and an auto reverse capability for a continuous reverse cycles. According to the 1971 Dutch Akai magazine, the M-10 is the X-200D with a main amplifier. And indeed the upper fart of the front is exactly the same. The M-10 has a three speed capstan motor and no speed change sleeve any more. This means, it couldn't run on 15 ips. The M-10 also has a 2x20 W main amplifier and has two integrated circuits 'on board'.
The M-10 has been available with both wooden and leather finish.
Of course a treble and a bass control knob is present as well as a three mode equalizer switch and a double headphones output just like the older M-9. The picture comes from the original M-10 flyer and was kindly given to me by Ian Gardiner from Christchurch, New Zealand.
The M-11 was the last set from the M-series and it is a bit of a stranger. The most striking difference between the M-11 and the older sets is the tape operation knob. The M-11 is the only Akai set which has a single knob for tape operation. This might be a copy of Sony. Since a lot of Sony sets used a single knob operation (until the TC-399 in the late seventies). This was much more complicated than the two knob sets which Akai has made for many years.
The M-11 has three heads but it doesn't have a three head system. It has one erase head, one combination GX recording/playback head for the forward direction and one GX head for reverse play. There aren't many Akai sets with a combination recording/playback head (only the GX-1820D and the GX-1900D come to my mind) so this is very rare.
Although a head which was pulled down by a solenoid was much more common in those days, it would have been too complicated in a mechanical single motor machine with no other solenoids.
The M-11 has an auto stop/auto shut off switch, a 2 mode tape selector switch for using either normal or S.R.T. tapes, a speed selector and two separated. The M-11 has two speeds: 3.75 ips and 7.5 ips. The M-11 has four belts including the counter belt, which means it's going to be difficult to find a good working one without worn belts after about 30 years.