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The 600-Series

All Akai models from the 600-Series are 10.5" capable sets. The later models have a 6 head configuration and can record and playback in both directions. The popular GX-635D is the base model of the 6-head sets.

The first set from the 600-Series is the GX-600D, produced between 1975 and 1976; the last set is the GX-646, produced between 1982 and 1984. Although the GX-400D was the first model from a new 10.5" line, Akai never continued that series; something which still amazes me. They choose a new series of model numbers instead which became the 600-series.

The GX-630D is probably the most popular example from the 600-series and many units were sold. Most of the sets from the 600-series have a high resale value.

The GX-630D was available in regular 4 Track versions, and the GX-630D-PRO a 2 track version, and the GX-630D-ss, 4 channel Version.

The GX-600D transport was heavily based on power relays and spark quenchers; while the GX-650D and later GX-630D sets transports used more transistor-transistor logic, like many pre-IC Logic machines.

The GX-620, GX-625, and GX-635, GX-636, GX-646, and GX-747 all came later, and used the proprietary IC Logic for the transport operational control functions.

GX-600D/DB/PRO (1975-1976)

This 3-head set is the first one from the 600-series; it looks a little like the 7" version GX-286D but has the mechanical push buttons like the GX-230D. However it's not a mechanical set: the GX-600D has an additional solenoid for engaging the brakes; the GX-230D hasn't.

The GX-600D and GX-650D sets preceed all of the other sets in the 600 Series, the GX-620, GX-630D, GX-625, GX-635D, GX-636, and GX-646 despite the abberation in the numbering scheme. While one thing all 600 Series sets have in common is that they all take 10.5" reels, beyond that, these sets are quite different. The GX-600D is perhaps the early predecessor of the GX-630D.

The GX-600D's look reminds me of somewhat of the GX-370D, and it is a mid-1970's set. Its a unidirection transport which uses an older type 2 Speed 4/8 Pole Hysteresis-Synchronous motor, the HM2-16MC as found in some lower end GX-2xx sets, along with a belt drive to run its single flywheel with center capstan.

There were three versions, the GX-600D deck with 1/4 track heads; the GX-600DB with Dolby B built-in, and the GX-600D-PRO with 15 ips and 7.5 ips and 2 Track Stereo heads. Since each of these was a 3 head machine, the GX-600D-PRO would NOT be able to play back 1/4 track tapes.

The GX-600D models are also the only sets from the 600-series with a belt-driven single capstan. Although most 10.5" sets have the power transformer on top-middle, this one has the power transformer beneath the left reel motor.

The GX-600D has all the common switches which you would expect from an Akai. It has an extra sound-on-sound function and it has also been available in a version with Dolby noise reduction, the GX-600DB and a two-track high speed version, the GX-600D-PRO.

The older 1975 Akai magazine says the GX-600D is the "living room version" of the GX-400D, which means the GX-400D was intended for semi-professional use.

GX-630D/DB/PRO (1976-1979) and GX-650D (1976-1979)

Both GX-630D and GX-635D are probably the most popular Akai sets from the 600 Series. Although its model number is higher, it's the earlier version of the GX-620 and it also is the 10" version of the GX-270D but without auto-reverse. The capstan motor is a direct drive type and it has two speeds, 3.75 and 7.5 ips. Its functions are almost identical to those be which can be found on the earlier GX-600D set, only the S.O.S. function has been omitted.

Just like the GX-600D, the GX-630D has been available in a Dolby version, the GX-630DB and also in a 2 Track Stereo version, the GX-630D-PRO. This GX-630D-PRO has a thicker capstan spindle and the higher running speeds of: 7.5 and 15 ips.

The GX-650D is absolutely the more professional version of the GX-630D and might also be the successor of the GX-400D, although it was not available in a 2 Track Stereo version. This set has 3 speeds (3.75, 7.5 and 15 i.p.s.) and a belt driven, dual capstan mechanism.

The GX-650D main motor is the servo-controlled, model SCM3-16TW. Both pinch rollers are activated by their own solenoids, there's another solenoid to pull the tape guides and another one to release the brakes. The tape path is symmetrical. The GX-650D is one of the only sets which has a Hall Effect Sensor near the left reel motor which checks if the left reel table is still in motion. By means of this sensor, a quick change between tape functions can be accomplished.

Finally, this 4 track, 2 channel set has an S.O.S. switch and a cue function.

The GX-650D uses the same Servo-Controlled Capstan Motor and belt drive system to power two flywheels with dual center capstans at 15 ips, 7.5 ips and 3.75 ips, as in the GX-400D, GX-400D-PRO, GX-400D-ss, and PRO-1000. Behind the reels, the GX-650D has the outer-rotor reel motors later found in the GX-630D.

Yet, unlike the other later Akai sets with the exception of the Servo-Control Board, as seen in the GX-400D, the GX-650D has no PC boards in common with any other Akai.

GX-650D Specifications

Track system: 4-track, 2 channel stereo system

Tape speed: 3.75, 7.5, 15 ips.

Total Wow and Flutter: Less than 0.055% @ 7.5 ips

Frequency response: 30 to 30,000 Hz +/-3 dB @ 15.0 ips (Akai LN tape)

30 to 26,000 Hz +/-3 dB @ 7.5 ips

30 to 20,000 Hz +/-3 dB @ 3.75 ips

S/N ratio: Better than 58 dB @ +6 VU

FFWD/RWD time: 120 sec. using a 2400 ft. tape

Main motor: SCM3-16TW Servo-Controlled Motor

Reel motors: Eddy current outer rotor motor; model: 24XO-TD


Erase Head: E4-260

Recording head: R4-200 (GX)

Playback head: P4-202 (GX)

Dimensions: 524 (H) x 442 (W) x 258 (D) mm.

Weight: 26.2 kg.

Power consumption:

Listed new: $ 1330.00 in 1976

GX-620 (1979-1982) and GX-625 (1980-1982)

Just like the GX-255 is the newer version of the GX-270D, the GX-620 is a new version of the GX-630D. It's technique is like the GX-255 and it also has the IC logic controlled function buttons. This is the only Akai deck with the tape counter integrated in the head cover.

Only the United States models have an additional pitch control function; all the other models haven't.

The GX-625 is a more sophisticated version of the GX-620 and it has some additional features. Any GX-625 has a pitch control function and it was the first Akai model to have a Digital LED Electronic Tape Counter, which counts the reel revolutions as well as hours/min/sec.

Unfortunately the min/sec counter doesn't work during fast winding. But the Digital Tape Counter can be programmed to provide auto-stop, auto-play, and auto-repeat (block repeat) functions. Basically the digital counter setting is put into memory, and when the point is reached, it Rewinds until it gets reaches the lower number, Stops, and goes into Play from that point.

When the program functions are activated, the GX-625 uses its SCR Electronic Brake Assist System: During rewinding the tape starts to slow down at counter position "0020" or so (depending on tape speed). When the counter reaches "0000" the tape has almost stopped.

Finally the common mechanical brakes are engaged and the tape stops at "0000" exactly. When the program functions are not activated, the GX-625 uses the mechanical brakes only.

On the back of the unit there's an socket for a 12 V. DC adapter, which is meant to keep the counter position in memory once the power is turned off.

GX-625 Specifications

Track system: 4-track, 2 channel stereo system

Tape speed: 3.75 ips and 7.5 ips

Total Wow and Flutter: Less than 0.03% @ 7.5 ips

Frequency response: 30 to 26,000 Hz +/- 3 dB @ 7.5 ips (WR tape) 30 to 19,000 Hz +/- 3 dB @ 3.75 ips

S/N ratio: Better than 62 dB @ 7.5 ips

FFWD/RWD time: 120 sec. using a 1.800 ft tape

Main motor: SCM-200

Reel motors: Eddy current outer rotor motor; model: 24XO-TD


Erase Head: E4-201

Recording head: R4-241

Playback head: P4-251

Dimensions: 446 (H) x 440 (W) x 241 (D) mm.

Weight: 17.6 kg.

Power consumption: 120 W. max.

Listed new: $ 720.00 in 1982

GX-635D/DB (December 1978-1981), GX-636D/DB (1981), and GX-646 (1982-1984)

These sets are almost identical. One thing they all have in common is a symmetrical 6 head design, which allows the user to play and record in both directions; something which is similar to the 7" GX-260-series.

The GX-635D/DB is the first set from these series and is probably the first Akai set with IC logic controlled tape function controls. Externally it looks a little like the GX-266D; it also has the holes in the head cover. However, some GX-635D/DB sets do not have the holes in the head cover (see pic. #1). The GX-635D/DB has a pitch control function, rec mute with a 1 sec. timing led and a timer start switch for making recordings during absence.

This set also has the ability to mix line and mic signals since it has separated line-in level knobs. These knobs have a memory ring. This ring turns along when the line in knob is turned up, but it remains in that position when the line in knob is turned down again.

The GX-635D/DB was the first Akai set with a mechanical real-time counter in minutes/seconds (only at 7.5 ips). When you use the 3.75 ips speed you have to multiply the time on the counter by 2 to get the real elapsed time. A reverse selector and a remote control socket on its rear are also present.

This set has also been available with built-in Dolby encode/decode pcb's and a switcheable multiplex (MPX) filter, the GX-635DB See second picture). This Dolby version lacks the timer start switch. This set has been extremely popular an still has a high resale value.

GX-635D Specifications

Track system: 4-track, 2 channel stereo system

Tape speed: 3.75 ips and 7.5 ips

Total Wow and Flutter: Less than 0.07% @ 7.5 ips

Frequency response: 30 to 27,000 Hz +/- 3 dB @ 7.5 ips

30 to 20,000 Hz +/- 3 dB @ 3.75 ips

S/N ratio: Better than 65 dB

FFWD/RWD time: 75 sec. using a 1.200 ft tape

Main motor: SCM200

Reel motors: Eddy current outer rotor motor; model: XO24-TD


Erase Head: E4-241 (x2)

Recording head: R4-241 GX head (x2)

Playback head: P4-251 GX head (x2)

Dimensions: 483 (H) x 440 (W) x 256 (D) mm.

Weight: 21.0 kg.

Power consumption: 70 W....150 W (depending on location)

Listed New: $ 960

The GX-636/DB is almost identical to the GX-635D/DB. Externally the GX-636 looks more like the GX-266II and it lacks the glossy front panel looks, which makes it a typical early 80's straight-looking set. The GX-636 has no other functions than the GX-635D and the 12 holes in the head cover are gone. The differences between the 635 and 636 are mostly internal impovements. To service the GX-636, you need the GX-635D service manual plus some additional 636 sheets.

The pcb layouts are a little different. This set has also been available with Dolby N.R. as the GX-636DB.

The letter "D" behind the model number has been omitted since Akai didn't make any sets with a built-in main amp anymore.

The GX-646 is the last set from the 600-series. It is the successor of the GX-636 and has the capability to use Extra Efficiency tapes (EE). It also has an additional bias adjust control on the front panel.

The GX-646 has not been available with Dolby N.R. Internally both GX-636 and GX-646 are very similar but again some improvements and cosmetical changes have taken place. While the GX-636 has the "standing" VU meters, the GX-646 had the "hanging" VU meters. The GX-646 has a three mode timer start switch, while both GX-636 and GX-635 had a two mode timer start switch.

This page is under construction ( Like software, the job is never done!....)
Last Update - 2-7-2004 5:00 PM.

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