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Old 1st May 2011, 09:08 PM   #1
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Default Akai tapedeck capstan rpm

Hi all

Still working on my Thorens TD165 .... Just discoverd today that the motor has a wobbely axel so it has to leave the party

Found a nice old AKAI tapedeck beyond repair with a great AC motor...
Not only took the motor but also the flywheel /capstan combination and the supply trannie.

The motor reads 110 volt 1500/1800 rpm 50/60 HZ
In Holland we have 230 volts 50 Hz.....

So hooking all up the motor run smooth and powerful.

Now to the question # 1..... If the motor runs @ 1500 Rpm...It's pully will run @ 1500 rpm....
How can I calcullate (or what is) the RPM on the Capstan/Flywheel combination?

Is it near 300 RPM?

Question 2.....how can I regulate (electronicly) that nice Akai motor...

Question 3..... I want to lose the heavy trannie.... But also need to "lose" 147 volts AC... Can I hook up an Capicator in series?......what value should I use?

Would like to hear from you all

Feel free to follow the resauration proces on adservices.nl

regards Auke
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Old 2nd May 2011, 04:27 PM   #2
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There are two ways to work out the RPM of the capstan.
1) Measure the diameter of the capstan shaft, calculate the cicumference (pi d) and divide this figure into the tape speed (assuming you know it) x 60. There will be a small correction factor for tape thickness but this is likely to be insignificant on a domestic machine.
2) Measure the diameter of the motor pulley and the capstan pulley / flywheel, divide the larger measurment into the smaller and multiply by 1500. I assume a simple single stage idler or belt drive.
You can`t run a synchronous motor with a series cap from a higher voltage supply, you`re stuck with the transformer unless you get an electronic drive which can handle this. The only way to regulate the speed of a synchronous motor is to vary the drive frequency. There may be available a drive system that will give both the voltage and frequency control that you need.

Barry
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Old 3rd May 2011, 08:02 AM   #3
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Thanks Barrymagrec,

It sure makes sence the way you do the calculation...

After some concideration and in combination with your answer I think I have figured out a way to get what I want...

What I have got is that nice AKAI motor, It's seperate flywheel, and my TT platter.
The TT platter has a diameter value witch does not change, so does the Flywheel.
The driven side of the flywheel also.
So if I do the RPM calculation backwards..... from Platter to flywheel and from flywheel to motor drive shaft and start calculating with 78 RPM I have to come up with a Driveshaft Diameter/RPM

Combining this with a amplifier (80 watts) and a variable sinwave as input (your electronic drive), I should be able to vary the speed of my platter from 78 RPM, via 45 RPM downwards to 33.3 RPM.

Could this be the way to go?

Regards,

Auke
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Old 3rd May 2011, 10:59 AM   #4
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The problem with your scheme is that you cannot normally alter the drive frequency of a synchronous motor by the amount you need. With a motor rated for 50 / 60 Hz it is likely that at say, 40Hz you would get significant overheating due to the extra current it would take, unless you reduced the input voltage. You may also get audible noise problems from the windings. Running it at higher frequencies, say 75 Hz will reduce the current giving a loss of torque which may or may not be a problem but bear in mind that synchronous motors normally give far less torque until they are up to synchronous speed. I would expect that going much below 40Hz or above 75Hz would not be practical and this would not give you the range from 33.33 to 78 rpm in a single stage. Do you really need 78? Does the Akai mechanism have some form of mechanical speed change for different tape speeds?
Sorry to appear so negative but what you propose will not be simple to carry out - good luck.

Barry
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Old 3rd May 2011, 11:26 AM   #5
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Barry,

You are not at all Negative. You are simple pointing out the pros en cons...

The flywheel has got a 50/60 hz adjustment as does the motorpully...
basicly what you are suggesting is to stick with motor speed...run it at 100volts, no adjustment there and make the speed changes on the pully's the mechanical way.... prefebly on the flywheel and motor driveshaft with the help of a leaver of some kind...

It is worth to investigate and will safe money and effort in the electronics department
Auke
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Old 3rd May 2011, 11:44 AM   #6
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Yes, what I actually had in mind was that you could have a "centre" speed of , say 39 rpm at 55 Hz and electronically go +/- 15% to give you 33.33 and 45. Using the mechanical change to double the speed would then cover 78. This should not give any electrical problems with the motor. If you are actually interested in very old recordings they can have been recorded at anything between 75 and 80 rpm so a degree of adjustment may be usefull.

Barry
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Old 3rd May 2011, 11:55 AM   #7
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Thanks Barry

Your proposel is a slight adjustment of what my second idea (my last post) was...

You say.... Run the motor at 55 hz on a pure sinwave... make sure to have 39 rpm at the platter.... electronicly adjust the motor drive frequentie for 33.3 and 45 Rpm platter rpm.
Mechanicly Double on the platter rpm by changing the belt position on the motor drive shaft/flywheel pully... Taking in account I would need 78 rpm....If not just make sure the electronic are setup as discribed...

Makes perfect sence Barry

Thanks...
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