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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 22nd Mar 2023, 11:32 am   #41
AdrianH
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Default Re: AKAI M-9 Tape recorder/player.

I will be taking the unit apart later today as I am hoping for some replacement 8 Ohm speakers to arrive, and I want to check bias currents in the output pairs.

I can try the superglue idea as a way to keep them together for a while.

I guess that taking the cams out is a major task?

Adrian
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Old 22nd Mar 2023, 12:04 pm   #42
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Default Re: AKAI M-9 Tape recorder/player.

If you are experienced in mechanical strip downs, I would say it is quite straight forward as long as you take careful notes/take many photos. As referenced in my previous Post sometimes disturbing the cams, especially unscrewing the securing screw (for ones that have screws) can lead to the cam breaking apart.

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Old 22nd Mar 2023, 3:06 pm   #43
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Default Re: AKAI M-9 Tape recorder/player.

The reason for the moving heads is the two coils on each erase and bias head are always in circuit in series, i.e. no switching is involved.
For mono use the unwanted pole is moved out of the tape path.
Same used on the Akai X2000 reel/8-track/cassette deck,
unusual machine with the one motor driving everything !
The crossfield bias system was patented by Tandberg and licenced to Akai.
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Old 22nd Mar 2023, 4:24 pm   #44
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Default Re: AKAI M-9 Tape recorder/player.

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Originally Posted by Restoration73 View Post
The reason for the moving heads is the two coils on each erase and bias head are always in circuit in series, i.e. no switching is involved.
For mono use the unwanted pole is moved out of the tape path.
Same used on the Akai X2000 reel/8-track/cassette deck,
unusual machine with the one motor driving everything !
The crossfield bias system was patented by Tandberg and licenced to Akai.

Given the comparative complexity of this mechanical arrangement, wouldn't it have been a whole lot cheaper (and less fault and wear prone) to instead have used a bit of extra switching (relay?) and a "dummy"-head inductor to achieve the objective electronically? The bias head would, of course, still have needed to be moved horizontally away from the R/P head to allow tape threading, but surely less faff than all that faffing around with bound-to-wear cams and metal steps?

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Old 22nd Mar 2023, 5:01 pm   #45
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Default Re: AKAI M-9 Tape recorder/player.

If you only record in stereo, nothing has to move. I would think the speed change mech
on an idler wheel turntable was subject to greater wear, but all seemed to survive.
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Old 22nd Mar 2023, 7:52 pm   #46
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Default Re: AKAI M-9 Tape recorder/player.

As far as I know there is no horizontal adjustment with the Bias Head and no requirement to move the Bias head when tape threading.

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Old 22nd Mar 2023, 8:02 pm   #47
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Default Re: AKAI M-9 Tape recorder/player.

There is a actuator that allows the bias head to move close to the tape in record and holds it away when it is in play/FF/RW.

If I wanted to just record stereo, I would need to jack up the erase and bias heads to a fixed 3.5mm height as that is what the cam would have done.
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Old 22nd Mar 2023, 10:58 pm   #48
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Default Re: AKAI M-9 Tape recorder/player.

Quote:
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There is a actuator that allows the bias head to move close to the tape in record and holds it away when it is in play/FF/RW.
Presumably also holds it away in "Stop" position?

Mike
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Old 22nd Mar 2023, 11:07 pm   #49
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Default Re: AKAI M-9 Tape recorder/player.

Quote:
Originally Posted by Boulevardier View Post
Quote:
Originally Posted by AdrianH View Post
There is a actuator that allows the bias head to move close to the tape in record and holds it away when it is in play/FF/RW.
Presumably also holds it away in "Stop" position?

Mike
Yes that is correct.

The replacement speaker did not arrive today so I have not had another play with the AKAI.

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Old 23rd Mar 2023, 7:57 pm   #50
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Default Re: AKAI M-9 Tape recorder/player.

Quote:
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The reason for the moving heads is the two coils on each erase and bias head are always in circuit in series, i.e. no switching is involved...
Yes and the series setup in the bias head mean individual record bias adjustment for left and right tracks was not possible. You had to hope that the bias was equal. The only other method was fractionally tilting the bias head after loosening its two mounting screws........................... But again the fundamental problem of Xfield bias wasn't just its increased complexity but its exaggeration of momentary high frequency sound dropouts, often due to dirt on the tape surface. With conventional bias, any dirt on the tape oxide surface lifted the tape off the record head leading to some dropout. But since the bias was also reduced, there was at least some compensation due to some reduction in "over bias". Xfield bias reversed that, further over biasing the tape which was the last thing you needed. The system had an inherent tendency to record level instability. Fortunately, playback was unaffected.

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Old 23rd Mar 2023, 9:06 pm   #51
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Default Re: AKAI M-9 Tape recorder/player.

Looking at the cam picture in #28, it might be possible to attach it to the spindle by a split
pin right through the spindle. Now the height of the rod that engages with the cam steps might be
adjusted by altering the position or size of the ball bearing at the end of the rod - it is the ball
that causes the groove marks in the cam steps surface.
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Old 24th Mar 2023, 2:06 am   #52
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Default Re: AKAI M-9 Tape recorder/player.

In my search I found a cam as pictured in #4. It appears unworn, so may have been a
spare part. The only difference is the fixing screw hole is 90 degrees from the picture,
putting it in a larger area of metal - perhaps this was done to improve strength.
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Old 24th Mar 2023, 4:12 am   #53
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Default Re: AKAI M-9 Tape recorder/player.

Continuing the theme of ideas for a repair to the cam, killing time in a hobby store this morning I saw for sale brass collars with a pre-tapped metal thread and the correct Allan screw and wrench included. They came in various imperial sizes. I took a quick photo below.

I wonder if this would be useable if bonded to the remaining cam and epoxy built up around it and the cam for strength. As the collar is made of brass, strength at the screw area should well exceed that of the original metal used by Akai. Perhaps a brass band or strip could be fashioned to bond to the outside surface of the collar and extending either side to the undamaged edge of the cam for added strength.
An advantage of this approach would be that precise adjusting of the cam's height and angular position on the shaft would be no more difficult than with the original factory cam.
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Old 24th Mar 2023, 8:52 am   #54
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Default Re: AKAI M-9 Tape recorder/player.

I did wonder about making a brass bush milling out the broken area and soldering it in place, but it was suggested that the cam would probably dissolve, so I have not done any more with the 4T cam at present after seeing the state of the rest of the cams.

For a machine that was given to me to see if it could be passed on to raise a bit for charity there were no takers so I am not sure how much money or time I want to put into it.

Still awaiting some replacement speakers to see what it sounds like and to confirm if both channels are OK, with luck the speakers may arrive today. I guess it is something to play with, just wish it did not weight as much.

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Old 24th Mar 2023, 9:05 pm   #55
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Default Re: AKAI M-9 Tape recorder/player.

The speakers turned up today so at least both channels are working now, I looked at the quiescent current and could not get it down to the 28mA as suggested in the manual, but I did manage to get it balanced evenly. Played a bit of Edith Piaf, not that I could understand the words but it sounded OK.

Stuck a bit of a video up perhaps I may get some leads on Cams from the US who knows.

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