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The GX Head Technology Units

Next came the harder Ferrite / Ceramic Head Technology. A separate page later on, shows the details of the single Crystal Ferrite Core and Precision GX Glass Surface which defines this technology. Here is a picture of the GX-365D, which was the first AKAI Reel to Reel tape deck made in this "GX" series, using these superb "Glass Heads". This was a new variation on the Ferrite/Ceramic surface that some other tape deck and tape recorder manufacturers have also used ( Tandberg, Teac and Sony come to mind ). But growing a single crystal ferrite core appears to have had multiple advantages and probably was at first a bit costly. Incorporating the outer glass surface I believe is quite unique to Akai GX Heads, but the result is less friction, and perhaps is more resistance to ferrite surface and edge chipping than in the conventional ferrite/ceramic surface heads ( gap erosion/edge cracking is a known failure mode in the conventional ferrite heads with use, over time )..

The GX-365D probably dates from 1969, with delivery worldwide in 1970, and it instantly became the high-end unit; replacing the X Series models. Chronologically it preceeded many sets which have lower numbers, by almost a decade, but there is no accounting for the Akai Model numbering system... Numerically, it comes after the X-360D, which had the conventional heads and crossfield head biasing, and yet it still retains the GX-365D and the GX-365, with its built-in hybrid power amplifiers and stereo speakers basically had the same look and feel of the prior X-355 and X-360D.

The Model GX-365D has an auto-reverse function which uses a moving head platform, so physically the Playback head moved using a solonoid for precise and repeatable movment. At the same time, a relay reverses the tracks, instead of incorporating an additional Reverse Playback Head. I guess the early GX heads were quite expensive to make, and this complicated moving platform was easier, and more cost effective to implement than adding a second stationary playback head.

Among the less desirable aspects of the early Akai RTR's - they use a lot of power, and also have a number of known failure modes. Some of the most expensive parts which can fail, being their Power Relays. Most of the ones used were complicated 4 Pole devices, even if all four poles were not actually engaged. That is the electrical equivalent of 4 internal switches going on at the same time. These parts have a plastic cover, which tends to seal them off from the environment, but they are not actually hermetically sealed. As a result, these relays do become affected by the effects of oxidation, air pollution, high humidity, sea salts, and also the arcing of the internal contacts over time.

With tens of thousands of cycles of repeated use over time, internal arcing from the high power transfer of power to the inductive high voltage AC motors can take their toll on even the best gold-plated sets of contacts. This is worse under humid conditions, or in the precense of pollutants, which causes the contacts to become pitted. Basically, small lightning like arcs of power burn away the thin contact surface ( which even on the best power relays is still a rather thin layer of gold plating ). In which case, the normally low impedance between these moving contacts then becomes a high impedance, an intermittant, or no contact. Also another failure-mode, the contacts can and do become welded solid, remaining together resulting from the high transfer of power ( usually only if the spark-killer associated with a relay happens to fail, which is another problem that is sometimes seen ).

Either way, relays with pitted or welded will no longer function to initiate the operational states, and then the set will no longer function. In either case, these parts would have to be unsoldered, removed, and replaced, preferably with new relays, having gold contacts, and also having the same ratings for the contacts and for the coil mechanism. Today these types of power relays typically cost $12. to $18. each, so to replace all [ 13 ] of the GX-365D's Power Relays is a considerable investment of about $150. to $225. in parts alone... along with quite a few hours of labor. Yes, a number of other things can also go wrong in these older sets; in the power supply, and elsewhere, as they are approaching 35 years of age. Yes, they will have their breakdowns, and repairs can and do become expensive. Often, costing several times what the set is worth.

Later on, Akai started to use more and more transistors, and fewer and fewer of these 4 Pole Power Relays, in the operational circuits, most notably the savings were in the later sets which used a full logic controlled solonoid operational system. This was first and formost due to the cost of these Power Relay parts, and being electromechanical devices, their eventual high failure rates. The GX-400D three or four years later only uses [ 8 ] Power Relays; while the later GX-266II uses only 3 Power Relays, and 2 other smaller relays; the maximum economy was inched out probably in the GX-255 which only uses 2 Power Relays and a couple of smaller relays.

Just along the same lines, as the 70's wore on, the Akai sets became lighter, and the full Walnut Veneer cases became "Wood product covered with durable wood grain vinyl material" or in English... plastic coated simulated walnut grain. My own 400 Series sets are a case in point, my GX-400D-ss has a true walnut veneer case, while my GX-400D has a plastic coated simulated walnut grain case. Later came formica imitation walnut side panels and metal tops and bottoms. Then even the metal tops and bottoms as found on the GX-266D/267D/266II gave way to plastic tops and bottoms on the GX-255; GX-620, the GX-625, and others. Yes, the bean counters won.

Here is the vintage GX-365D:

Several years later, and featured on the cover of Akai Magazine in 1973, came the GX-370D; it was the first 6 head function set, using two of the Combo heads for erase and record and one GX Play Head on a moving platform. Yes, it is somewhat derived from the GX-365D, as it uses the moving head platform technology, and it also has some features seen in the 280 Series a year or two later, specifically, the locking solonoid controlled Pause Control ( a feature which is sorely lacking in the GX-260D - which doesn't have a pause control at all! Exactly why the follow-up sets abandoned the solonoid pause control for a more simple mechanical pause could be a cost cutting factor, I see no advantage to the less reliable, poorer performing mechanical pause system.

The GX-370D being a 3 motor unit is also fully solonoid controlled, using lots of relays, in fact it actually has two more solonoids than most sets - one for the head movement, the other for the pause system. Also making its first appearance here was the lighted Operational Control Buttons, with feather touch switches. This was also seen in the later GX-400 and GX-255, as well as the GX-620, and GX-625. Most Akai's lack lighted control buttons, some later sets have leds, but the GX-370D's lighted controls are a nice touch here. So all in all, the GX-370D was a pretty nice and innovative unit - for an early GX set. It has the full 4 sided real walnut wood veneer case, it is a staggering 55 lbs. heavy, and built to last, unlike later sets with their metal, then plastic, and walnut simulations...

Here is the GX-370D:

Reverting back to the low end, and continuing in the GX Series in a more numerical count, as far as I know, there was only one Akai GX Reel Deck made which used a simple one motor mechanism, along with a single knob operational block ( very similar to those found on many Sony Reel to Reel decks ). This set was both unique, and puzzling: Model GX-M11D. It featured a centered capstan, and auto- reverse, and style wise, I'd call it mid-to late 1970's, but little else is known about it. That is a very nice Dust Cover, only one I've seen where the Akai logo is used as a handle....

Here are pictures of another slightly unusual unit, a GX-1900D it has GX heads, and also a built-in Cassette Deck, and you can record or transfer music in either direction between them:

Here is a picture of an early vintage GX Series unit the GX-215D:

Here is a picture of an early vintage GX Series unit the GX-220D:

Here is another picture of a GX-220D:

Here is a picture of an early vintage GX-225D:

Here is another picture of a GX-225D:

The GX-230D was my first Akai, that I purchased new around 1975, and it still works great ! This is a 3 motor deck which had the Combo Erase/Record head, as is also seen in the GX-265D and a few other sets from the mid-1970's. The GX-230D used the P4-202 Playback Head, which can also be found in the GX-270D.

The Operational Mechanism of the GX-230D is mostly mechanical, with its mechanical interlocking controls, it outward look does seem to be much like the later sets, like the GX-265D, GX-270D, and GX-630D, but that is where the similarity ends. In reality, it has more in common with the dual levered 4000 Series than would appear on the surface. Depite its true mechanical nature, one of its best features is its solonoid operated pause control.

The operational switches force down levers and some mechanical linkages, much like in its forerunner, the two knob operational block sets. So, it is certainly not fully solonoid controlled in the same manner as the GX-370D, or the IC Logic controlled GX-255, or other later sets the GX-620, GX-625, GX-635D, GX-636, or GX-646. Due to the mechanical nature of its mechanism, it lacks the remote control capability, and it also lacks the ability to switch between a fast wind operation and Play, without first going through Stop. It also lacks 1/4 track mono capability, since it doesn't have separate record buttons for the Left and Right channels ( unlike the GX-255 or GX-265D and most of the the higher end sets ).

Here is a picture of an Akai GX-230D:

This photo is not my actual GX-230D, but it sure looks the same!

I consider the GX-255, to be perhaps, the pinacle of the mid-priced 7" reel decks, the Akai shown here basically used the same electronics and mechanical design as the higher-end GX-620D, GX-625D, and GX-635D sets, which were the 10.5" reel versions. The GX-255 was not directly imported into the USA as far as I know, and so, it is not seen that often. One feature which really sets it apart, from most similar models in the GX-2xx line, is its partial smoke grey clear head cover, and the matching smoked grey ( lighted when operational ) Operation Block Controls - which are really neat ! I'm especially fond of the green blinking Play Button during the "Pause" function. The GX-255 has the later IC Logic based operational controls as can be found on the GX-620D, and GX-625, two sets which have a fairly similar look to the GX-255. Still, if you look closely, you'll see that the two 10.5" sets have the pinch roller situated above the capstan, as the various GX-630D sets also do. Note that GX-6xx sets are all 10.5" reel capable. Something else that sets the GX-255 apart is, that in a four-head configuration ( auto-reversing in playback only ) deck, it uses the same later model heads ( perhaps by the numbers, even later heads than are found in the much revered GX-747 and GX-747dbx ). Specifically, the GX-255 has the R4-242 Record Head along with the P4-251 Playback Heads. It also uses a high end capstan motor model SCM-200B, which, from the "B" designation probably means it is a revised/improved version of the capstan motor found in the highest end of the Akai's, the: GX-620D, GX-625D, GX-635D, GX-636, GX-646, and GX-747 decks. Interestingly, the GX-230D, and the GX-255 both have a solonoid operated pause control, a design which is not found on some of the higher-end auto-reverse / reverse recording decks, such as the six head: GX-265D, GX-266D, GX-266II, and GX-267D.

Here are three pictures of the 1978 vintage GX-255:

Here is a picture of an early vintage GX Series unit the GX-260D. The GX-260D is a perplexing set. First off, it has no Pause Control. But it does do continuous reversing, a function which is missing from the set that followed it: the GX-265D. I believe it was the first six head function set, to have a center capstan and thus a fully symmetrical tape path. It does use the combo erase/record heads, but it uses a belt driven motor, so its definately one of the last of the old-school sets for Akai.

Akai's which came in the later part of the 1970's, used various Servo-Controlled / Direct-Drive Capstan Motors, which allowed Akai to add a variable speed control ( for altering the pitch on playback ). While any of the Servo-Controlled sets, such as the GX-230D, 250D, GX-255, GX-265D, GX-266D, GX-267D, and GX-620D was capable of this variable speed, most of these sets didn't have the front panel pitch control. Still some of the later sets ( GX-266II, GX-625D, GX-635D ) and apparently some later GX-620D's did have a front panel +/- 6% speed pitch ( on playback only ) adjustment. It could be a neat gadget to have, as one would use it if the tapes played where recorded off-speed on some other machine. Using Servo-Controlled/Direct-Drive Capstan Motors, did give better Wow and Flutter performance figures than in most of the prior belt-drive systems, so that could be considered its' main advantage.

Here are pictures of an early vintage GX Series unit the GX-265D:

There are several similar sets later in the GX-260 line, which all feature basically the same electronics and somewhat similar mechanical designs. Mechanically the GX-265D does resenble the GX-230D to some extent. On a functional note, when foil activated reverse is initiated, on both the GX-230D and the GX-265D this simply reverses the direction of the capstan motor, without stopping. Later sets have an intermediate function, where the pinch roller is disengaged for nearly 2 seconds during which time the capstan motor changes direction, then the pinch roller is re-engaged. Its a "Clink, Hmmm, Clink" process that takes about two seconds to complete and I guess it doesn't mean much, but it is present on the later 266D/267D/266II sets, which are closer to the high end GX-620D, GX-625D, GX-635D, 10.5" Reel versions.

The above GX-265D, and those sets that followed, use a symmetrical head configuration, with a center capstan drive. The GX-265D uses two of the combo erase/record heads, while later sets: the GX-266D, GX-267D, and GX-266II all use a true 6 head configuration, with auto- reverse, continuous reversing and reverse-recording initiated by using foil activated sensing posts.

Here is a picture of a 1978 vintage GX Series unit, the GX-266D. Looking much like its close relative, the GX-267D, they are very difficult to tell apart... except for the head cover, the GX-266D has 18 holes in its head cover, the GX-267D has none:

The six head sets could also do continuous reversing, for repeat play, and reverse recording. The last three GX-26x models are the 7" reel versions, while the 10.5" reel versions, the GX-620D, GX-625, and GX-635D's seem to only differ basically, in the number of details. The GX-265D, GX-266D, and GX-267D lack the remote control socket on their rears, and they use the SCM-2-24KJ capstan motor, which is also found in the much more middle-of-the-line GX-230D. The GX-266D, GX-267D also have numerically much earlier heads, the R4-240 Record Head, and the P4-240 Playback Head. One nice thing, the GX-266D, had true VU Meters, the ones with the black pointer and yellow background, and scale from -20 to +3 dB. The later GX-266II, despite some added features used an annoying looking VU Meter with an expanded -20 to +8dB VU meter scale, and it had a green pointer against a white background ( very much like the meters present on the GX-255 ). Perhaps the worst flaw in the various GX-266 / GX-267 sets, is that they all employ a mechanical pause control. Here, a micro-switch initiates the brakes about halfway down as you engage the pause switch, while the Pinch Roller is lifted just a few millimenters from the tape. When disengaging, you don't quite get that true instantaneous "blip-less" full-speed start that you get from the sets which use a separate fast-action solonoid to engage the pinch roller when you disengage pause. It is this which is perhaps the only significant flaw in the design of these mid-high end GX-266D / GX-267D / GX-266II, 6 head, 7" Reel sets.

Here is the GX-267D:

Evolving to the final version in the 7" reel, 6 head design, within the GX-2xx Series, we come to the GX-266II, which incorporates three additional features: 1) The capstan motor found in the GX-635D and higher numbered sets in the GX-6xx Series. 2) A Remote Control Socket on its rear. 3) The front panel +/- 6% Pitch Control to adjust the Servo-Control in Playback mode. A refinement over the GX-266D/267D is the twin stationary (reverse) sensing posts, wheras the prior sets had one stationary post on the left, and one sensing post on the moving right tension arm, which is prone to failure, much like the similar right tension arm that is found on the GX-400D.

Cosmetically, I do prefer the black button accenting and contrasting seen on the GX-266D/267D to the GX-266II's all-silver/no contrast look. Still, the record and playback heads of the GX-266II seem to have also evolved one iteration numerically from the prior sets: the R4-241 record head, the P4-251 Playback head. Just how much the large numerical jump in Playback Head designation effects a sound improvement in the GX-266II as opposed to the GX-266D/267D is very difficult to know. But in general, record and playback heads that are higher numerically, do have a better frequency response specification, as listed in the Service Manuals.

Truth be told, both the GX-267D and the GX-266II use some of the best circuitry in the audio path, no IC's, not even for the headphones. Some of the other sets use an IC here and there, and for the most part, those more expensive later designed sets, for all their fancy features ( specifically the GX-255, GX-620, GX-625, GX-635D, GX-636, GX-646, and GX-747 all use an IC for the headphone output, which I think limits the sonics, and also the output headroom... at least from the headphone jack. The GX-267D and GX-266II instead use a simple complementary-symmetry output stage, after multiple single-ended stages and for some reason ( or maybe for that exact reason, it simply sounds better than some of its brother and sister sets ). The later GX Heads, those with higher numbers, are found in the later machines, which are usually the more expensive models. Other than those half a dozen differences, the GX-266II appears to be quite identical to the prior GX-266D, and the GX-267D. While I don't care much for the "revisionist" VU Meters found on the GX-266II... What can you do? The second picture is a closeup of these VU meters on the GX-266II...

Here is a picture of a 1979 vintage GX Series unit the GX-266II:

The GX-270D is a set very much like the GX-230D, but it seems it has the full solonoid controls much like the GX-265D. Though I've never owned one, I've been advised that the GX-270D does have the feather weight control buttons ( like on the GX-370D and many later sets ) but otherwise, it is basically the GX-230D with solonoids. If I had been doing the numbering, I think it should have been called the GX-235D. Its main claim to fame is a small Red "Peak" Led, seen just between the VU Meters ( which isn't that much of a feature if you ask me... ). Other than that its a standard middle of the line Akai, with four head function, & Auto-Reverse in Playback only.

Here is the GX-270D:

All sets in the GX-280 line appear to predate many other sets with lower numbers ( specifically: the GX-230D, GX-255, GX-265D, GX-266D, GX-267D, GX-266II, and GX-270D ). Despite their model numbers being somewhat higher, there isn't much to distinguish the 280 Series, except maybe a rather nasty propensity for breakdowns. They are all 3 motor decks amd seem to suffer more than their share of relay failures, spark killer failures, transistor, and diode part failures ( lots of diode failures I've been told ).. They are early 1972 vintage and have the plug-in circuit boards, which makes for easy servicing, but also adds an additional level of possible failure mechanism's as these circuit board edge connectors can break or fail, and can be near impossible to replace.

The GX-280D and GX-285D have the "moving platform" playback head, which sits on a solonoid for reverse playback, as can be found on some of the very earliest Akai auto-reversing sets, and is perhaps a throwback to the days when it was cheaper to include the whole solonoid / moving mechanism, than to use an additional GX playback head.

Here is a picture of the GX Series GX-280D:

The most desirable set in the 280 Series of these is the GX-280D-ss, which is a 4 Channel / 2 Channel usable set. When in 2 Channel mode, it has auto-reverse without the moving head mechanism. But in the 4 Channel realm, it lacks high-end 4 channel features like Simult-Syncing ( called Quadra-Sync by Akai ) as found in the GX-630D-ss and GX-400D-ss. Last two sets in this series, the GX-285D, and GX-286DB both incorporate the Dolby B noise reduction system. The latter model designation minus the "B" which was included on the GX-286DB, GX-630DB, GX-635DB, and GX-636DB the last sets to have internal Dolby B.

The GX-285D has a backframe, with 9 plugin boards, and the early SCM-24 Servo-Motor with the large external detector head. The method of controlling the capstan servo-motor speed is also unusual, in that a discriminator coil ajustment is used to adjust the slower speed, while a potentiometer is used for adjusting the higher speed. So these 280 series sets can be considered perhaps rather quirky sets. They also used the early GX R4-200 Record Head, and the P4-200 Playback Head, which they shares some features and functions with the earliest sets from the late 1960's. It could have been the first, consumer machine to incorporate Dolby B Noise Reduction System ( if not it was certainly among the first ).

Here is a picture of the GX Series GX-285D:

The GX-280D-ss can be found among the 4 Channel Quad setsHere

The last set in the 280 series, the GX-286DB is not often seen, but it is was somewhat more evolved, and was unique for being the only Akai Reel to Reel set to include non-moving touch switches in the Operation Block. These switches are of a capacitance sensing FET controlled design, like those found on some Art-Deco Elevator Systems. I'm really not sure why this type of switch controls was never used again, perhaps there was some licensing problem, or it was found to be susceptable to blow-out or failures, all I know is the elevator systems I've seen, seem to be working fine, decades later, but I have no data on their repair rates.

Here is a picture of the GX Series GX-286DB:

The GX-400D line consists of exactly one set, but boy it was the real high-end for the Akai line. I say that because it used the same chassis and motors as are found in the GX-400D-ss and the PRO-1000. Rumour has it that the GX-400D was limited to a production run consisting of just 200 units, I can't deny that, or confirm that. This series was definately designed to appeal to studio's and radio stations, as well as high end home users, along with the GX-400D-ss version which was basically a Studio in a box, and the PRO-1000; a 2 Track version with more advanced microphone mixing which could be considered a "poor mans" Studer. Tipping the scales at nearly 69 lbs., within such esteamed lineage, the GX-400D shares the same 3 speed servo-controlled motor; 15 inches per second; and a closed loop dual flywheel assisted capstans within a belt drive system that rivals Studio Tape machines for low wow and flutter; also probably the biggest VU Meters ever seen in a tape deck; along with a set of audio controls that all tick off in minute increments. There are two cosmetic variations, the beige VU meters and the blue; the latter can be seen to match cosmetically some of the Akai Receivers and amplifiers of the period.

About the only thing the GX-400D lacks is internal Dolby "A" or even Dolby "B", or "C" noise reduction, well I guess they did have to build it to a price-point. It does feature a distortion reducing non-defeatable ADR Circuit that reportedly reduces distortion in the upper two or three octaves. As a benefit, it also has a record and playback frequency response that is flat almost to 30,000 Hz. at both 15 ips and 7.5 ips, which is no small feat! The only thing I fault it for, is the huge mechanical "Thunk" when it goes into Play, as both pinch rollers hit the capstans. Well just maybe that is elitist nit-picking :-). Still... some users will certainly jump for joy, at a machine that has such a frighteningly loud way of announcing... "I'm going into Play now "... THUNK... which then reverberates off the four walls of the room ( only if your room actually has four walls... ). On the slight down-side, its "logic" circuitry really isn't, its just eight of those costly 4 Pole Power Relays, which in reality can get a bit troublesome after a decade - or two, or three deacdes. Also the head changing switch is not sealed, and oxidation and can become rather troublesome, causing the wrong heads to be active, or losing the head interconnection completely - giving no sound in reverse, or forward play.

Both the Head Switch, and numerous Power Relays, are this design's weak points. That neither is quite environmentally sealed off does mean they are exposed to air pollution, sea salts, and other pollutants over the years; and then they become troublesome. The GX-400's feather touch operation switches which are all lighted ( except for Stop ) and the solonoid pause control, with the dual capstan mechanism - its a blast. Tape handling is both gentle and impressive as its keeps tight control of the tape between those precision balanced flywheel assisted capstans running between a 1/2 inch wide flat belt. It allows a more precise head to tape contact than can be engineered into a single capstan moving tape system. Also a tighter stop to startup nominal speed deviation compared to what one can find in lessor sets. Some interesting brochures and data can be found on the PRO-1000 Page about these functional aspects. The clear benefits of a dual capstan mechanism certainly defines these sets ( also the identical twin GX-400D-ss and PRO-1000 mechanism's - same capstans, same flywheels, same motors, same belt drive system ) as being in a higher class than even the rest of the set. So functionally, operationally, and audibly its pretty much the tops... While I can't get a peep out of mine in Reverse Play mode, I haven't yet wished to dismount and disassemble it, to clean those head switch contacts; it is a ton of weight, as well as, a ton of work.

Here are some pictures of the GX-400D:

Go to the next Akai Vintage photo page The GX-600 thru GX-747

Go to the prior Akai Vintage photo page The 4000 Series

This page is under construction ( Like software, the job is never done!....)
Last Update - 4-9-2003 11:00 AM.

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Steven L. Bender

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