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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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10th Apr 2005, 10:39 am | #1 |
Nonode
Join Date: Feb 2005
Location: Worcestershire, UK.
Posts: 2,534
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Using 60Hz gram motors on 50Hz supply
At http://www.radiocraft.co.uk/restoration3.htm I say...
To adapt it for our UK 50Hz supply two neoprene shrink sleeves were later added to the capstan (on the left end of the bearing seen here) to increase its radius. The final speed achieved was spot-on 78 rpm. However I do suspect that this 60Hz-rated motor may run at a higher temperature when fed from a 50Hz supply. Can someone tell me, is this a reasonable assumption to make - or have I missed something ? (The driving voltage remains correct btw.) Thanks, Steve |
10th Apr 2005, 10:55 am | #2 | |
Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,861
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Re: Using 60Hz gram motors on 50Hz supply
Quote:
It was certainly common practice with a lot of decks frpm the 50s and 60s (which usually used shaded pole induction motors) for the manufacturers merely to supply different diameter pulleys to adapt them to different frequency mains supplies. Nick. |
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10th Apr 2005, 11:58 am | #3 |
Rest in Peace
Join Date: Apr 2003
Location: Edgware, North London.
Posts: 307
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Re: Using 60Hz gram motors on 50Hz supply
Steve
The current taken by the motor will depend to a large extent on the supply frequency because of the reactive component of the motor's impedance. This is the AC "resistance" which increases with frequency, so that at lower frequencies the motor will draw more current. Consider the ultimate low frequency ie zero, or DC. The current would only be limited by the resistance of the windings and would get very hot indeed! So at 50Hz its likely to get hotter than when running at 60Hz. The same applies to transformers. Joe |
11th Apr 2005, 2:05 am | #4 |
Retired Dormant Member
Join Date: Apr 2003
Location: Salt Spring Island, BC, Canada
Posts: 368
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Re: Using 60Hz gram motors on 50Hz supply
All you can do is to run the motor for about an hour and then feel it. If you can keep your hand on it then it is OK. If you burn your hand then a rethink is due. A 10 watt power amplifier driven from a crystal derived 60 hz to power the motor?
John. |
11th Apr 2005, 6:02 pm | #5 | |
Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,861
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Re: Using 60Hz gram motors on 50Hz supply
Quote:
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11th Apr 2005, 6:32 pm | #6 |
Nonode
Join Date: Feb 2005
Location: Worcestershire, UK.
Posts: 2,534
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Re: Using 60Hz gram motors on 50Hz supply
I had also considered compensating for the lower reactance by adding a high power resistor in series and therefore running the unit at a voltage on the low side. But this of course would have reduced the torque.
In actual fact, the 'pulley size' was changed, the motor was hand tested for warming (but I never felt it warm up to more than hand-hot), a thermal fuse was added and the unit went out to the customer with a warning to play only one or two records at a time. Thanks to everybody for their advice. Steve |
11th Apr 2005, 10:00 pm | #7 |
Administrator
Join Date: Dec 2002
Location: Cardiff
Posts: 9,072
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Re: Using 60Hz gram motors on 50Hz supply
That sounds OK then. The motors on 1970s BSR decks get so hot that you can't hold them for more than a couple of seconds when running correctly!
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12th Apr 2005, 8:20 am | #8 |
Retired Dormant Member
Join Date: Dec 2003
Location: Solingen, Germany
Posts: 727
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Re: Using 60Hz gram motors on 50Hz supply
Good morning,
two years ago I had to solve this problem for a customer. He has an american clock. With an xtal you never get exactly 60Hz over a long time. The mains frequency is controlled to make it possible to drive a clock motor from it. My idea was to lock the 50Hz mains with the generated 60Hz via PLL (VCO frequency 600Hz) It is explained in the picture. It works very good. When I made this thing I did not know the 4046 hi hi. How do you like this idea? Kind regards Darius |