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AR77 Motor


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Hoping some of the more clued up electrically proficient members might offer some insight here.

 

I have an AR77 turntable - ~ mid 80's which I believe makes it an XB77, one of the last XBs made (according to Dave at Vinyl Nirvana), that I am beginning to restore.

 

Upon pulling it apart, I discovered a Haydon motor, 115v, 60Hz  (300RPM) - not totally surprising.

What is surprising, for the life of me I cannot find a transformer in the circuitry at all. There is what appears to be a .67mF cap across the terminals, and that is all.
The back of the unit clearly states 220V - 50Hz, and I'm led to believe this was an AU delivered / sold unit.

 

But further adding to the mystery is that the two prong US style plug has had the flat prongs twisted in order to fit AU plugs. Scary stuff.

What puzzles me .... it works. I plugged it in, and it appears the speed is correct, the motor isn't getting warm or showing signs of having 240V up it's bum when it's not meant to.

So ... how is it that the speed is correct and a 115V motor is running happily (and correctly) off 240V without a transformer?

 

I have found what I believe to be a suitable 240V Hurst replacement motor (3001-005):

http://www.hurst-motors.com/aabdirectdrive.html

 

It's got me stumped at the moment though.

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Since it is a low powered motor,it can be used on 240V mains supply with a suitable series resistor.Around 4k7 Ohms with a 10 W rating should be a ball park value.The motor pulley needs to be of a larger diameter to adjust the speed to correct for the 50 Hz mains frequency and the phase shift capacitor  also changed to suit.Of course this work  may have been performed by the manufacturers and the labelling is correct. 

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A couple of caps and no transformer is standard for the XA/XB series in my experience. As is the plug you describe. I've had a few and never an issue. You may also find that even in 'idle' - as in, as long as it's plugged in - the motor oscillates ever so slightly and emits a small hum. From my research, this is considered 'normal'. I believe I found a thread on this on VE if you're interested.

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All of the Rega and Linn 240 V models used a 110v motor, Earily Regas used a cap as an AC resistor to perforn the voltage drop and second cap to do the 90 degree phase shift for the cosine winding. It sounds like the AR uses a similar setup.The ony reason they switched to a resistor later on was because resistors were cheaper.  The motor will still operate at any frequency from around 42 Hz to 68ish Hz, and usualy has a voltage tolerance range of -15/ +10 %. If it starts and runs at correct speed, all is well.

Edited by Number 9
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Thanks for the input all. The motor is noisy and has loads of end float, so it has to be replaced.

 

My theory of using a 230V won't work then, as the pulley would be the wrong size if my understanding is correct.

 

I should be able to find an exact match however in 110V which would be fine.

 

This is the only component in the circuitry (other than a small cap on the switch).

 

post-103433-0-19151200-1404779354_thumb.

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Hi Marc, have you contacted Dave at Vinyl Nirvana? Bit of an AR guru in the states, may have some info to help. He also sells a new mega buck improved Hurst for AR models, although I am unsure whether he has the pulley for 240v operation.

 

Steve Frosten helped me tremendously when I did up an XB. Supplied an armboard to suit Rega arms, springs, studs and tons of info. He has restored countless ARs from what I can see. He can be easily contacted through the Vinyl Engine site - where you will also find a few examples of his work - and I can try dig up his email address to pm you

 

I have heard of belt driven Thorens owners using 16v motors and controllers from Pro-Ject with success - pretty similar design to the AR so another possibilty perhaps?

 

At any rate I'll be watching your resto with interest! I still have an original 2 motor [yech...] XA in pieces in a box awaiting attention

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I have a old Premotech motor that you can have. I'll need it for a couple weeks while I test the 110/220v output modules for the standalone #9 tt computer. but after that you're welcome to it. alternately i have 24V Prem Motors available.

Edited by Number 9
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