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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 18th Apr 2024, 2:12 pm   #1
dougietamson
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Default Akai M7 project

I have an Akai M7 tape recorder that has seen better days.

My 1st issue is the pinch roller with dry cracked rubber.

Is there anyway to get it back to life or must it be replaced?


Doug
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Old 18th Apr 2024, 6:15 pm   #2
knobtwiddler
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Default Re: Akai M7 project

If you can restore that roller back to use I will be very surprised. If you can't find a reissue roller (check around - there are repro rollers on Ebay, although be careful about quality), there is a fellow in the US who re-rubbers rollers. He's done a couple for me: https://www.terrysrubberrollers.com/

I'm not aware of anyone else offering the service.

Considering how tatty this roller looks, you could try your luck with acetone. You never know. I've seen some people try to sand their rollers using fine paper, but it never results in good wow performance.

NB - I bet you Terry's re-rubbered a few M7s before.
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Old 19th Apr 2024, 11:48 am   #3
dougietamson
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Default Re: Akai M7 project

Thanks KT, I'm sure he has, they sold a lot under the Roberts brand.
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Old 19th Apr 2024, 11:54 am   #4
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Default Re: Akai M7 project

While I wait for Terry to let me know what he can do and how much it costs I thought I'd try some DIY on the pinch roller so I can check the rest of the mechanicals.

I used a ring of rubber cut from an old inner tube and luckily it fitted just right.

I then 'smoothed' it out using fine grit wet and dry with it mounted in the lathe.

No glue used yet, I have some black rubber glue for repairing speaker cones and bike repair kit glue. I'll check the motor run cap and try running the deck (amps not powered up) with some tape in it.
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Last edited by dougietamson; 19th Apr 2024 at 12:21 pm. Reason: added info
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Old 19th Apr 2024, 1:24 pm   #5
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Default Re: Akai M7 project

Time to check if the valves are all present and correct.

So we have 5 in the left ch amp:

6267 (special quality EF86)
12AD7 (low microphonics 12AX7)
6BQ5 (SE output amp)
6AR5 (bias osc on left channel only)
6X4 (rectifier)

same as above for the right channel except no need for the 6AR5 bias osc.

All look original NEC and Hitachi (though the 6267's have a thick rubber damper covering the label) except one of the 6X4 rectifiers is a Zearix Made in Japan.
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Old 19th Apr 2024, 1:39 pm   #6
DMcMahon
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Default Re: Akai M7 project

Appyling Glycerine can sometimes soften/rejuvenate some rubbers but your pinch wheel probably is too far gone.

David
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Old 19th Apr 2024, 1:41 pm   #7
dougietamson
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Default Re: Akai M7 project

Here's some close-ups of the NEC 12AD7 valves, not seen one before.
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Old 22nd Apr 2024, 12:00 pm   #8
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Default Re: Akai M7 project

I was going to offer you one from my spares deck but...
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Old 22nd Apr 2024, 5:35 pm   #9
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Default Re: Akai M7 project

Quote:
Originally Posted by Welsh Anorak View Post
I was going to offer you one from my spares deck but...
Do you think the damage to the pinch wheel rubber is caused by cleaning with IPA?, the internal rubber parts are all ok.

Glyn, I might have a DIY idea for the spare pinch roller.

I found some rubber spacers on Amazon, only £5.69. Maybe they could be modified to fit the metal part with a bit of work on the lathe.

The OD of the roller just needs to be close enough to the original to make contact with the capstan (inc the tape speed add-on bushing)

link to amazon

https://www.amazon.co.uk/Purpose-Thi...CB9RXJ2D&psc=1

Doug
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Old 22nd Apr 2024, 9:44 pm   #10
Analogue man
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Default Re: Akai M7 project

Quote:
Originally Posted by dougietamson View Post
Quote:
Originally Posted by Welsh Anorak View Post
I was going to offer you one from my spares deck but...
Do you think the damage to the pinch wheel rubber is caused by cleaning with IPA?, the internal rubber parts are all ok.]

Doug
No IPA will not do that, unfortunately some of the rubber compounds used in the past were less than long term stable while others seem to last forever.
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Old 23rd Apr 2024, 9:57 am   #11
Welsh Anorak
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Default Re: Akai M7 project

Luckily the roller on my good M7 is still in fairly good shape.

I use something called Platenclene which I've found cleans without damage, though the roller needs to be in serviceable condition first!
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Old 23rd Apr 2024, 2:30 pm   #12
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Default Re: Akai M7 project

Quote:
Originally Posted by dougietamson View Post
The OD of the roller just needs to be close enough to the original to make contact with the capstan (inc the tape speed add-on bushing)
Just to veer into generalities for a moment; it's the capstan that sets the tape speed isn't it? So as you say, the pinch roller just needs to hold the tape against the capstan (where diameter matters for the angular velocity) so the rubber diameter is not crucial as long as it's not too tight, or not making contact.

By contrast, when the capstan wears down it's necessary to make sure a repair is the right diameter?
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Old 23rd Apr 2024, 2:52 pm   #13
dougietamson
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Default Re: Akai M7 project

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Quote:
Originally Posted by dougietamson View Post
The OD of the roller just needs to be close enough to the original to make contact with the capstan (inc the tape speed add-on bushing)
Just to veer into generalities for a moment; it's the capstan that sets the tape speed isn't it? So as you say, the pinch roller just needs to hold the tape against the capstan (where diameter matters for the angular velocity) so the rubber diameter is not crucial as long as it's not too tight, or not making contact.

By contrast, when the capstan wears down it's necessary to make sure a repair is the right diameter?
That's what I've read, the M7 also had a 15ips option but needed a smaller OD pinch roller and a larger OD capstan adapter. The original roller would 'pinch' up too close otherwise.

Photo attached of an original Akai 15 ips kit.
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Old 23rd Apr 2024, 10:43 pm   #14
TIMTAPE
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Default Re: Akai M7 project

Quote:
Originally Posted by Analogue man View Post
Quote:
Originally Posted by dougietamson View Post
Quote:
Originally Posted by Welsh Anorak View Post
I was going to offer you one from my spares deck but...
Do you think the damage to the pinch wheel rubber is caused by cleaning with IPA?, the internal rubber parts are all ok.]

Doug
No IPA will not do that, unfortunately some of the rubber compounds used in the past were less than long term stable while others seem to last forever.
Some advise not to use IPA as a rubber cleaner due to the long term risk of drying out the rubber. Instead water and a little dishwashing liquid is recommended. However sometimes when the rubber hasn't been so regularly cleaned it can take something a lot stronger than said water and detergent to remove stubborn muck built up on the roller and other tape path parts.
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Old 24th Apr 2024, 10:56 am   #15
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Default Re: Akai M7 project

Good morning Doug,

I have come across a box marked Akai bits and in there is a pinch wheel, the rubber of which looks fine.

The shaft is different to yours in that it has a step but that may be not an issue.

Using my schoolboy ruler, the o/d of the rubber is 40mm, 10mm thick and the overall height is 20mm. The step is about 4mm on the spindle which is 9mm o/d and 6mm i/d.

If this any use you are welcome to it free of charge.

Kind regards,

David
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Old 24th Apr 2024, 11:17 am   #16
dougietamson
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Default Re: Akai M7 project

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Originally Posted by captainpugwash View Post
Good morning Doug,

I have come across a box marked Akai bits and in there is a pinch wheel, the rubber of which looks fine.

The shaft is different to yours in that it has a step but that may be not an issue.

Using my schoolboy ruler, the o/d of the rubber is 40mm, 10mm thick and the overall height is 20mm. The step is about 4mm on the spindle which is 9mm o/d and 6mm i/d.

If this any use you are welcome to it free of charge.

Kind regards,

David
What a generous offer, thanks Dave.

I'll send you a pm and let me know your paypal details to cover postage and a coffee/tea/pint/whisky.

I can then continue with my idea to modify my existing dead one partially revived with a band of bicycle inner tube.

The tape mechanism seems to play ok with my bodged roller, no playback through amps yet, all valves removed.
I checked both the PT's, both HT CT winds are 250-0-250ac no load, filament winds are good too.
I then installed the 2 rectifier valves and ran it on the bulb limiter, both read 398vdc no load, filter caps visually look good. I'll run them for a while on the isolation transformer at 120vac to reform then full 240 (on the bulb limiter).

Doug
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Old 24th Apr 2024, 11:34 am   #17
Analogue man
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Default Re: Akai M7 project

Quote:
Originally Posted by TIMTAPE View Post
Quote:
Originally Posted by Analogue man View Post
Quote:
Originally Posted by dougietamson View Post

Do you think the damage to the pinch wheel rubber is caused by cleaning with IPA?, the internal rubber parts are all ok.]

Doug
No IPA will not do that, unfortunately some of the rubber compounds used in the past were less than long term stable while others seem to last forever.
Some advise not to use IPA as a rubber cleaner due to the long term risk of drying out the rubber. Instead water and a little dishwashing liquid is recommended. However sometimes when the rubber hasn't been so regularly cleaned it can take something a lot stronger than said water and detergent to remove stubborn muck built up on the roller and other tape path parts.
Interesting as it is well known that exposure to water over time will cause rubber to perish.
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Old 24th Apr 2024, 12:07 pm   #18
TIMTAPE
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Default Re: Akai M7 project

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Originally Posted by Analogue man View Post
Quote:
Originally Posted by TIMTAPE View Post
Quote:
Originally Posted by Analogue man View Post

No IPA will not do that, unfortunately some of the rubber compounds used in the past were less than long term stable while others seem to last forever.
Some advise not to use IPA as a rubber cleaner due to the long term risk of drying out the rubber. Instead water and a little dishwashing liquid is recommended. However sometimes when the rubber hasn't been so regularly cleaned it can take something a lot stronger than said water and detergent to remove stubborn muck built up on the roller and other tape path parts.
Interesting as it is well known that exposure to water over time will cause rubber to perish.
I found the reference below where they say: "Most elastomers undergo rubber degradation over time and the most common rubber deterioration causes are exposure to light, oxygen (ozone) and heat".

Good detailed information too on restoring rubber when that's possible.

https://www.martins-rubber.co.uk/blo...)%20and%20heat.
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Old 24th Apr 2024, 11:50 pm   #19
Analogue man
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Interesting reading, thanks.
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Old 26th Apr 2024, 9:29 am   #20
dougietamson
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Default Re: Akai M7 project

Quote:
Originally Posted by captainpugwash View Post
Good morning Doug,

I have come across a box marked Akai bits and in there is a pinch wheel, the rubber of which looks fine.

The shaft is different to yours in that it has a step but that may be not an issue.

Using my schoolboy ruler, the o/d of the rubber is 40mm, 10mm thick and the overall height is 20mm. The step is about 4mm on the spindle which is 9mm o/d and 6mm i/d.

If this any use you are welcome to it free of charge.

Kind regards,

David
A quick clean with diluted washing up liquid (mild green...) fits perfectly and it's running great.

Now I have a lot of caps to replace...
Thanks again Dave.
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