Align AKAI GX-365 reel tape deck

Discussion in 'GENERAL AV Discussions' started by JohnCPR, Mar 9, 2009.

  1. JohnCPR Enthusiast

    JohnCPR
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    I have rebuilt an AKAI GX-365 tape deck. The audio now works as expected. I need to align the playback head in both the forward and reverse directions. I have an MRL 7.5 ips alignment tape and the AKAI service manual. The AKAI uses a single playback head that is solenoid shifted in a vertical direction to play either the 1&3 or 2&4 tracks of the tape. Unfortunately, an inexperienced person has misaligned the head and the service manual does not follow the MRL alignment procedure. I can align in the forward direction but the reverse azimuth and signal level shows from 6 to 10 dB misalignment.

    What is a procedure I can use to align the head so that the difference between forward and reverse signal level is about 1.5 dB?
  2. TLS Guy Audioholic Overlord

    TLS Guy
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    First check zenith alignment. This is making sure the head is vertical. If you don not have a gauge for this you should make one. You need a gauge that will align the head perpendicular to the chassis.

    Now check the rotational alignment of the head. Mark the area of the gap with a grease pencil. Play a tape, and make sure the gap is in the middle of the area where the wax pencil mark is worm off.

    Now clean and demagnetize the head.

    Play the azimuth alignment section, for four track heads this is usually a 10 kHz signal. Play it with tape going forward.

    First do a coarse alignment by connecting a millivolt meter to the left hand channel output. Adjust the azimuth set screw until you get maximum deflection of the meter.

    Now do the fine (phase method) adjustment. Set the recorder to mono, so that the channels are coupled. Now repeat the procedure to set the meter to maximum deflection.

    It is essential to do the coarse method first to avoid phase errors of more than 90 degrees.

    Now see how the output in the reverse direction compares.

    Now those reversing tape decks were pretty low fi. One of the big problems with them was the ability to have good azimuth alignment on both directions.

    My best advice if there is a big discrepancy is to adjust to get the forward motion right, and manually turn the tape over, so the tape always runs forward. This is just like a recorder that does not have auto reverse.

    I assume you are using this machine for playback only and not record. If that is so you need to adjust playback equalization for the 7.5 and 3 3/4 ips speeds. Does you manual go into this.

    If you are using it to record, you will need to set record bias for the brand of tape you plan to use and adjust record equalization. I assume the manual goes into this.
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  3. JohnCPR Enthusiast

    JohnCPR
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    Thanks you so much for your help. It makes a lot of sense and sends me in the right direction. The Akai glass crystal head makes it difficult to find the precise location of the gap. Any light to make the job easier is reflected back. You probably already know that the MRL 7.5 ips alignment tape is multifrequency with 1KHz @ 0 dB to set dB meter 0, and 500, 8K and 16K @ -10 dB to adjust azimuth, plus a range up to 20KHz @ -10 dB for bandwidth adjustment. The documents from MRL provide tables to make adjustments for other speeds and tape fluxivity. This is probably overkill for me but provides confidence in accuracy. I do not expect miracles from the relatively low fi AKAI, just a reasonable alignment. Since the same replay head, shifted vertically, is used for both directions, I hope for a reasonable match. If not, one direction will have to do. This is good hands on learning experience for me.
  4. TLS Guy Audioholic Overlord

    TLS Guy
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    It sounds as if you have quite a project! The gap will be in the center of the head. So make sure the grease pencil mark rubs off symmetrically.

    My quarter track tape is Ampex. I have a 1/2 track 7.5 ips MRL tape. That has a choice of 16 kHz or 10 kHz for azimuth. I like around 15 khz for 1/2 track and 10 kHz for quarter track. I would try the 16 kHz fost since you don't seem to have a 10 kHz track on your tape.

    What are you planning to use this for?

    My open reel machines.

    [​IMG]
  5. JohnCPR Enthusiast

    JohnCPR
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    The MRL standard alignment tape does have a 10KHz @ -10 dB in the bandwidth alignment section.

    I am still on the reverse alignment and trying to understand why the reverse is much lower in volume -6 to -10 dB (left and right channel difference) than forward. During the forward test @ 1 KHz, the playback amplifiers (left and right) were set to 0 dB on the meter, corresponding to the standard level from the MRL tape. The head is the same and so are the electronics. The only difference is the head in reverse is shifted to correspond to the 24 tracks on the tape. I would have expected the signal level would be the same. Somehow, in reverse, the head is not registering the same signal strength from the tape as well as up to 3 dB difference from left to right channels. Is this because the gap is not contacting the tape dead center for both directions and the reason for your grease pencil gap test? Does this mean the head needs to be twisted slightly on the y axis so that both forward and reverse volumes are about equal?
  6. TLS Guy Audioholic Overlord

    TLS Guy
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    Without me being there it is hard to say.

    The first thing is to do the alignments I suggested. The grease pencil is very important as it will tell you if the head is rotated, and if the head is the correct height. May be the head is too high or low. The head top head needs to be at the top of the tape. I wondering if you are picking up some of all four tracks forward and not all of two and four in reverse.

    The tape guides can also be a problem causing tape skew.

    If you can get it to work well forward, with good frequency response and no bleed from channels 2 and four, I would call it good and turn the tapes over.

    There is a very good reason why no good reel to reel machines ever had auto reverse, and that I have never owned an auto reverse machine.
  7. JohnCPR Enthusiast

    JohnCPR
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    Unfortunately, I do not have a grease pencil at present, so I shall get one. I do have a transparent 1/4" leader tape that allowed me to align the top edge of the tape to the top edge of the top core head for forward play and the lower edge of the tape to the bottom edge of the core head when in reverse play. This should ensure that the separation between tracks is adequate and as instructed by the AKAI service manual. There is still up to 10 dB difference between forward and reverse. I will try the grease pencil first. All other things being equal (electronics, head, & tape), the difference is how the tape presents itself to the head from one direction to another or perhaps the housing, being on a separate mount from the chassis for the y axis head positioning mechanism, slightly rotates due to tape friction. Unfortunately, there is no fine adjustment for this. I may have to losen the screws holding the head to the housing and ever so slightly rotate by trial and error. AKAI may mount the playback head so the position of the head around the y axis presents itself not for maximum signal in one direction but slightly offset so the source signal is approximately the same in both directions. Perhaps the fine pickup coils in the head are direction sensitive. As long as the head position remains fixed as set, the playback amplifier can be adjusted for the required 0 dB level.
  8. TLS Guy Audioholic Overlord

    TLS Guy
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    There is one more important thing to check before rotating the head, and this is a big problem with tape recorders. The issue is tape tension. Tape tension is very important. Too much and excess wow. Too little and poor head contact and low output.

    I'm wondering if the tape tension is low in reverse. That is something to check right away.

    Is that recorder a single or three motor machine? I hope it is not single, as they are the very devil to get in adjustment in this regard.
  9. JohnCPR Enthusiast

    JohnCPR
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    The AKAI is dual motor, one each for forward and reverse. There are also tension and electric brake adjustments. I will look for the instructions for tape tension in the AKAI Service Manual.
  10. TLS Guy Audioholic Overlord

    TLS Guy
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    Does it have a capstan motor separate from the spooling motors? Good machines have a capstan motor and then spooling motors under each reel hub, so they are three motor.
  11. JohnCPR Enthusiast

    JohnCPR
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    The AKAI DX-365 is a 59 lb machine with two large motors, the torque of which, from the service manual, are controled by varying the voltage to the motors using a bank of high power mutitapped resistors. One motor is used for forward, the other for reverse. These are controled by a bank of 13 relays and a timing sequence that maintains delay between the different modes of operation. This provides reasonable tape tension together with the voltage torque control for the contra rotating motors. One relay has been replaced over a small burn hole in the circuit board. I am fortunate in that the relays are still functioning. Whoever repaired the machine before I was given it by a friend did a sloppy job that I have managed to rectify. This is a challenge worthy of vintage car classification.

    Using the MRL tape, the frequency reponse is not within specifications. That is probably also due to gap missalignment. Marking the head gaps with a grease pencil should help me to determine whether the tape is moving over the center of the gap. I believe I will need to twist the head about the y axis in any case to obtain a reasonable balance between forward and reverse signal levels. I have crayons but where do I get the grease pencil you refer to and what color is best?
  12. TLS Guy Audioholic Overlord

    TLS Guy
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    What drives the capstan? Is there a place I can download a service manual for that machine? If I had one, I think I would be a lot more help to you.

    If the frequency response error is HF roll off, then the problem is likely a head alignment and or a tape tension issue. If the response is lumpy bumpy, the the issue is almost certainly a playback equalization issue.

    Don't be surprised if the machine rolls off in the bass. Almost all Far Eastern machines do, no matter what the specs say. The Far Eastern heads were never the quality of the European ones, especially the Studer/Revox heads, which were the best tape heads ever manufactured by far.

    After you have this machine under you belt, you should consider restoring a Revox, then you will really have a machine!
  13. JohnCPR Enthusiast

    JohnCPR
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    This is my second attempt on this reply since the first appeared to have failed. It is probably fortunate since the message will be shorter. The AKAI GX-365 weighs 59 lbs with two large motors for forward and reverse. These are controlled by varying voltage levels for torque through multi-tapped power resistors plus 13 relays and timing sequences for smooth transition between functions. The tension on the tape in either forward or reverse is by the contra-rotating motors. I do not have a tension guage to verify how much is applied during operation. The tension appears to be OK.

    In dealing with the position of the gap in the playback head around the y axis, the grease pencil mark along the gap will make a judgement as to which direction to turn the head easier. However, I am not familiar with grease pencils. Where do I find these and what color is best?
  14. TLS Guy Audioholic Overlord

    TLS Guy
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    Did you see my last post? I got your previous message, so I hope you can see my reply. A Crayola will be fine. I like red myself.
  15. JohnCPR Enthusiast

    JohnCPR
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    This is my third try to post the reply. I hope it works this time. My AKAI GX-365 has two large motors. Both are controlled by voltage levels for tension using high power tapped resistors, timing sequences for smooth transition between functions, and 13 relays to switch the sequences in the required order. The setup could be time consuming if they did not function correctly. As for tape tension on the heads in both directions, there are two spring tension levers directly after the spools. The spring lever next to the reverse take up spool is followed by a stabilizer fly wheel. I do not have a tension guage. However, because both tension levers are approximately shifted by about the same amount when the tape is moved in either direction, I assume the tension must be roughly the same. Taking a closer look at the playback head, the angle of the tape entering the head does not appears to be the same on both sides. I tried loosening the screws holding the head on the top of the head housing to attempt a rotation, however, the fractional movement is not of much use. It means I would have to remove the head and housing from the base and try to rotate the head in the housing from the bottom, if that is possible. There is no instruction for this in the maintenance manual so I assume the whole head assembly is meant to be replaced as a unit.
  16. TLS Guy Audioholic Overlord

    TLS Guy
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    I have been getting all your posts. I'm not clear what drives the capstan, is it friction, belt, or is there a dedicated capstan motor?

    I would not muck with the tape head. From your description of the head, it sounds as if the tapes is not skewing the same forward as backward. This was always the Achilles heel of bidirectional tape transports.

    In view of this post, I would strongly recommend setting it up for forward only and turn the tapes over. I would bet that this machine always had huge variability of performance with tape direction.

    Do you have a wow and flutter meter? They are pretty much essential when working on tape machines. A meter that also has a frequency counter is useful also, for working on servo controlled capstan motors.
  17. JohnCPR Enthusiast

    JohnCPR
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    Sorry for all the repeated posts. I am new to this forum and did not realize there was a second page. Not all forums deal with posts the same way. The capstan is belt driven. I do not have a wow and flutter meter. I do have a dual trace scope, a digital and a small analog multimeter, and a frequency counter. I am familiar with AKAI tape recorders. Generally, when new, both forward and reverse work satisfactorily for the consumer. I used a protractor and small ruler carefully placed over the replay head. The tape angle on the forward side leaving the gap is about 2 degrees greater than that entering. Judging by the marks on the screws around the heads, someone has already fiddled with the settings and may have removed or replaced the heads. I already carefully resoldered the connection pins to the wires at the back of the heads because the previous job was very sloppy with lumps of solder.
  18. JohnCPR Enthusiast

    JohnCPR
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    I forgot to add that I am unaware of any manuals that can be opened online. I usually have to buy them from manual sellers. I can however photograph portions of the manual and send them to you.
  19. TLS Guy Audioholic Overlord

    TLS Guy
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    Sorry for the tardy reply, but I was tired out yesterday, after moving mountains of snow from Wednesday's blizzard in bone chilling wind chills, on the old tractor.

    I have been pondering your problem. Only fractions of a degree of head misalignment change the performance drastically, let alone two degrees.
    However without the manual and pictures, I don't think I can provide you sensible help.

    As you can probably tell I'm not a fan of Far Eastern tape machines. I have found them much harder to work on that European and US machines, and not provide comparable audio fidelity, nothing like.

    It was the introduction of Far Eastern consumer electronics, the presaged the decline of the West.

    So many fine firms, that made such beautiful gear were put out of business.

    In the tape arena the destruction of Brenell Engineering, Ferrograph, Vortexion, Ampex and Clark and Smith I have always held against their low price point mentality.

    Before the onslaught, Ferrograph made wonderful machines. Built like a battleship, theirs ads said, and they were. Then they had to try and meet the price points of the Far eastern onslaught. Trouble is if you are known as the battleship brand, and then the build quality goes down, people expect it of the insurgent. However the consumer expected the battleship at the Far Eastern prices.

    Every time I see posts like best receiver for under $300, or best sub under $200, I cringe every time.

    I do have a fax machine here at Benedict, but it does not have dedicated line, so have have to set it to receive faxes when I know when is coming.

    If you PM me we can arrange to have you fax the relevant parts of your service manual.

    I leave for our Eagan home tomorrow, and I will be back in Benedict Tuesday.
  20. JohnCPR Enthusiast

    JohnCPR
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    I had to take my PC to have a faulty RAM replaced. I am in the middle of editing a wedding video and creating a DVD so the RAM couldn't wait. I will also have to rebuild my PC because the faulty RAM has created a few problems in my OS. This means I will be off line for a few days. I managed to remove the replay head and rotate the head around the y axis slightly. Unfortunately, there is no fine adjustment for this. The screws holding the head housing at the bottom can be moved slightly in the baseplate holes that are slighly bigger than the screws. I am now slighly rotated too much in the opposite direction. I would have expected a change in the signal level in the reverse direction but it is still up to 10 dB lower in signal level than forward. I will mark the head with the grease pencil I bought yesterday. Perhaps the top of the head is slanting forward so that the reverse motion over the bottom part of the head does not have the same contact. Another curious problem is that I cannot find a gap. Can it be that the sensing area is over the whole front part of the head?

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