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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 21st May 2024, 9:56 am   #21
dougietamson
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Default Re: Akai M7 project

I've had a go at making a 15ips adapter 'kit' for the Akai M7.

I decided to remove 3mm (radius) from the perished rubber of the original pinch roller on the lathe, the one in the 1st post.

Next up to make a 12mm OD adapter from some 12mm brass bar and drill a 3mm hole.

The Akai M7 capstan is 3mm OD and the 71/2 ips adapter supplied with the M7 is 6mm OD and has an internal 3mm hole to fit the 3mm capstan.

To muddy the waters the M7 has switch for 2 motor speeds, hi and low.

The tape speeds with the 3mm capstan are 1 7/8th (low motor speed) and 3 3/4 ips

The tape speeds with the 6mm capstan adapter are 3 3/4 (low motor speed) and 7 1/2 ips

With the 12mm adapter we get 7 1/2 and 15 ips.
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Old 21st May 2024, 11:19 am   #22
Welsh Anorak
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Default Re: Akai M7 project

Looks good!
Is the EQ for 15ips the same as 7.5? If not some calcs are in order...
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Old 21st May 2024, 12:01 pm   #23
dougietamson
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Default Re: Akai M7 project

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Originally Posted by Welsh Anorak View Post
Looks good!
Is the EQ for 15ips the same as 7.5? If not some calcs are in order...
I was wondering about that!

The 'best' way unless I change some components out is record and playback at 15ips with the EQ dial set to 7 1/2.
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Old 21st May 2024, 12:33 pm   #24
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Default Re: Akai M7 project

If I remember from when I had one, I think the Akai capstan sleeves have a conical relief on the underside and the capstan has a vary small cone. ThE sleeve sits on the cone, being centred by it, and the sleeve is held with its axis co-axial with that of the capstan by the flat face of the sleeve against the flat face on the undeside of the securing nut. Without care over this, any tolerance in the inner diameter allows the sleeve to be offset from coaxial, creating flutter.

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Old 21st May 2024, 12:59 pm   #25
TIMTAPE
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Default Re: Akai M7 project

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Originally Posted by Welsh Anorak View Post
Looks good!
Is the EQ for 15ips the same as 7.5? If not some calcs are in order...
It depended. I believe the US NAB playback standard for 7.5 and 15 ips was the same. Whereas Europe's CCIR, later IEC had them different IIRC.

There was no record standard as such, just whatever record EQ pre emphasis achieved flattish response at the particular speed and normal bias.

If you want strictly accurate response there can be more confusion because tape oxides slowly improved over the years and older machines often couldnt cope with the higher than expected record bias and record amp headroom requirements.

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Old 21st May 2024, 2:04 pm   #26
dougietamson
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Default Re: Akai M7 project

Here's a close-up of the capstan and adapters.

The capstan is just a straight 3mm rod with a thread to hold the 6mm adapter as shown fitted in the photo.
I polished the 12mm brass adapter with T-cut

This Akai M7 dates from 1964, very similar to earlier models which were 'inspired' by an Ampex 600 sent to Japan by Roberts who badged the tape machines produced by Akai for sale in NA, Akai branded machines were sold in the ROTW.
The later Akai models in the early 1970s were designed and branded as Akai as the partnership with Roberts ended.
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Old 21st May 2024, 2:53 pm   #27
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Default Re: Akai M7 project

Interesting! I had a 4000DS about a decade later when I looked into making a 7.5ips sleeve for a friend who'd lost his. This machine had a conical 'radius' where the capstan diameter stepped up at its root. I wondered about it and measured the clearance of the sleeve over the capstan and realised that it was a precision centring feature.

Yours doesn't have one, so the sleeve will have to be a very carefully toleranced fit.

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Old 21st May 2024, 3:15 pm   #28
dougietamson
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Default Re: Akai M7 project

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Originally Posted by Radio Wrangler View Post
Interesting! I had a 4000DS about a decade later when I looked into making a 7.5ips sleeve for a friend who'd lost his. This machine had a conical 'radius' where the capstan diameter stepped up at its root. I wondered about it and measured the clearance of the sleeve over the capstan and realised that it was a precision centring feature.

Yours doesn't have one, so the sleeve will have to be a very carefully toleranced fit.

David
The main issue with the 15ips adapter is the pinch roller radius has to be 3mm less, they sold a kit with the smaller pinch roller together with the 12mm capstan adapter. If you use the original 3.75/7.5ips pinch roller it is already engaged with the capstan 12mm adapter while at stop/ff/rev.

I drilled the hole using the lathe in 3 steps, 2.5mm, 2.8mm and final 3mm. It is quite a tight fit on the 3mm captan. Getting it off again is the issue, I might try some 2000 grit wet n dry rolled around the 2.5mm drill bit shaft to allow me to remove it a bit easier.
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