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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 10th Apr 2005, 10:39 am   #1
Panrock
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Default 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
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Old 10th Apr 2005, 10:55 am   #2
Nickthedentist
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Default Re: Using 60Hz gram motors on 50Hz supply

Quote:
Originally Posted by Panrock
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
It may depend on the type of motor.

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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Old 10th Apr 2005, 11:58 am   #3
joe
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Default 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
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Old 11th Apr 2005, 2:05 am   #4
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Default 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.
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Old 11th Apr 2005, 6:02 pm   #5
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Default Re: Using 60Hz gram motors on 50Hz supply

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A 10 watt power amplifier driven from a crystal derived 60 hz to power the motor?
John.
It's been done - I think some of the upmarket turntables of the early 1980s used synchronous motors driven from an onboard high-power oscillator, allegedly to improve speed stability and reduce motor noise. But I think in this case, I'd risk changing the pulley size and keeping an eye (or hand) on the temperature
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Old 11th Apr 2005, 6:32 pm   #6
Panrock
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Default 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
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Old 11th Apr 2005, 10:00 pm   #7
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Default 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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Old 12th Apr 2005, 8:20 am   #8
oldeurope
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Thumbs up 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
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