The 1800-1900 and 2000-series
The 1800-1900 and 2000-series are the combination series: the models in the 1800-series have a built in 8-track, the 1900-series have a built-in cassette and the 2000-series have both.
Only the 1800-series consists of multiple models, the 1900- and 2000-series only have one model.
In the mid 70's the demand for combination sets decreased, probably because the 8-track didn't make it in favor of the compact cassette and the sale of cassette decks increased a lot.
By 1975 Akai quit the production of combination sets.
The 1800L, X-1800SD (ca. 1969-1972), the X-1810/D (ca. 1973-1974) and the GX-1820 (ca. 1974-1975)
The 1800L could be a little older than the X-1800SD since it runs on both transistors and tubes. Both sets only have one motor and the well-known two lever tape control operation. The 1800L has an artificial leather finish and a 4 W power amplifier and it has the ability to copy from reel to 8-track.
The X-1800SD is a little more sophisticated version. 'SD' stands for 'Super Deluxe'. It runs on transistors only and has the Cross Field recording system which uses a one micron gap head here. The X-1800SD has two huge feet which look a little like grips and well, maybe they are. A speed change sleeve is included to make it run on 15 ips. This model has a 6 W. power amplfier.
The X-1810/D and GX-1820/D are both nice looking three motor sets with auto reverse for the reel to reel section and a black face panel. These sets look very much alike, only their head covers and line in knobs are different. The mechanics are similar to those found in the X-200D, X-201D, GX-210D and similar sets. One other difference: the GX-1820 lacks the 1 7/8 ips speed.
They have both been available with a 2x 6W power amplifier.
1810 Specifications (reel to reel section only)
Track system: 4-track, 2 channel stereo system
Tape speed: 1 7/8 ips, 3.75 ips and 7.5 ips
Total Wow and Flutter: Less than 0.12% @ 7.5 ips
Frequency response: 30 to 22,000 Hz +/- 3 dB @ 7.5 ips
30 to 18,000 Hz +/- 3 dB @ 3.75 ips
30 to 9,000 Hz +/- 3 dB @ 1 7/8 ips
S/N ratio: Better than 46 dB
FFWD/RWD time: 80/65 sec. using a 1.200 ft tape at 50/60 Hz
Main motor: model 16X
Reel motors: Eddy current outer rotor motor; model: 24X0-II
Erase Head: E4-5
Recording/Playback head: P4-100
Bias head: B4-1
Dimensions: 450 (H) x 435(W) x 240 (D) mm.
Weight: 21.4 kg.
Power consumption: 110 W. for X-1810 and 95 W. for X-1810D
Listed new: $ 800.00 for X-1810D and $ 900.00 for X-1810 in 1973