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 Post subject: Changing motor or power supply on a Russian turntable
PostPosted: Jan Tue 24, 2023 5:07 pm 
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Joined: Nov Fri 05, 2021 2:56 pm
Posts: 128
Location: Brookline MA
Hi everybody,

I generally post for my radios repairs, and found out this forum is also for Phono repairs, so let's go for it!

I have the opportunity to buy a soviet-era Russian turntable that cosmetically looks amazing to me. Information on the model is here:
http://rr20.ddns.net/Item.aspx?ItemId=e ... 69&Lang=En

The person selling says that it was working well in Russian but never worked right in the US, speed is wrong. Sure enough, since Russia power supply (220v 50Hz) is not the same as in USA (120v 60 Hz), so the motor won't turn at the right speed. I'm considering getting it only if I can get it to work in the US without having to plug it to a power transformer.

More specifically,

1. Is there a way, with a combination of components, to drive the motor at the right speed with a power supply of 120v 60Hz?

2. Otherwise, can I graft a US motor on the Russian turntable? What are the key elements I need to look at to make sure this will be compatible? Is that generally possible or do I need some kind of standard reference? I do own many turntable motors I could use for this.

3. Assuming I manage to replace the Russian motor with a US motor, will switching between different speeds work right away or will I need to adjust the electronics as well?

Any help or insight is appreciated, as always!

Jonathan


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 Post subject: Re: Changing motor or power supply on a Russian turntable
PostPosted: Jan Tue 24, 2023 5:43 pm 
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Joined: Jan Mon 16, 2012 3:15 pm
Posts: 9671
Location: Brandon, Iowa USA
I wouldn't expect that you would get much useful feedback inasmuch as the Russians exported no entertainment products to the West; so there is going to be a dearth of first-hand experience.

Having said that, there are only so many ways to bake a phonograph turntable cake. It is likely possible, if you have the necessary mechanical engineering chops, to adapt a Western phono motor to a Russian turntable.

I haven't encountered many Russian phonographs, but the ones that I have seen tend to be basic but reliable in operation. Your Russian turntable probably isn't motor-strappable for 110V operation (since there was no intent to export these units to North America) but that can be resolved with an adapter transformer like the ones sold for personal-grooming appliances being travel-toted between the 110VAC world and the benighted souls elsewhere on earth that use 220V mains.

The AC frequency issue is a little more sticky: a synchronous motor that is intended to operate on 50Hz will be about 20% "fast" on 60 Hz. The only solution is to get the drive pinion turned down on a lathe until it provides the correct rotation speed at the turntable. No big deal technically; it's just simple proportional math.


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 Post subject: Re: Changing motor or power supply on a Russian turntable
PostPosted: Jan Tue 24, 2023 6:46 pm 
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Joined: Nov Fri 05, 2021 2:56 pm
Posts: 128
Location: Brookline MA
I see...

I was still thinking that for speed adjustments a good combination of resistors should work, wouldn't it? Pitch controls, at least in the MCS 6502 (same as Technics SL-23), are just a variable resistor and directly control the speed as far as I understand.


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 Post subject: Re: Changing motor or power supply on a Russian turntable
PostPosted: Jan Tue 24, 2023 6:57 pm 
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Joined: Jan Mon 16, 2012 3:15 pm
Posts: 9671
Location: Brandon, Iowa USA
johnnyjohnboy wrote:
I see...

I was still thinking that for speed adjustments a good combination of resistors should work, wouldn't it? Pitch controls, at least in the MCS 6502 (same as Technics SL-23), are just a variable resistor and directly control the speed as far as I understand.

Nope. Different motor technology.


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 Post subject: Re: Changing motor or power supply on a Russian turntable
PostPosted: Jan Tue 24, 2023 7:48 pm 
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Joined: Mar Thu 21, 2019 2:53 pm
Posts: 430
Location: Nicosia / Cyprus
A couple years ago a customer brought in for repair a 50 to 60Hz converter which was installed on an American jukebox. The mains supply in my country is 240V 50Hz. The jukebox is being used with a stepdown transformer. The converter has 2 circuits, an H bridge motor driver and a motor start up relay driver . Operation is as follows, on power up the relay feeds the motor directly while its driver is monitoring the motor current and as soon as the motor speeds up it changes over to the H bridge which is driven by a 60Hz oscillator. The incoming AC (120V) is rectified and feeds the H bridge with DC and then is converted to AC again , square wave though. So the unit operates on 120V 50Hz input and 120V 60Hz output. Apparently it could be used with 60Hz input and 50Hz output but in your case the motor is 240V.

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 Post subject: Re: Changing motor or power supply on a Russian turntable
PostPosted: Jan Wed 25, 2023 3:10 am 
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Joined: Sep Mon 16, 2013 1:42 am
Posts: 6140
Location: Tucson, Arizona U.S.A.
johnnyjohnboy wrote:
I see...

I was still thinking that for speed adjustments a good combination of resistors should work, wouldn't it? Pitch controls, at least in the MCS 6502 (same as Technics SL-23), are just a variable resistor and directly control the speed as far as I understand.

You might be able to correct the speed with resistors (emphasis on might) but that will result in greatly reduced torque. So the speed will likely be unstable. There is also the possibility of overheating the motor since induction motors don't like being run at reduced voltage. You still need 240 volts to run the motor and the amplifiers unless you replace them too.

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Who's that swimming in the punch bowl?
It's Walter Wart, the freaky frog!


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 Post subject: Re: Changing motor or power supply on a Russian turntable
PostPosted: Jan Wed 25, 2023 5:13 am 
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Joined: Nov Fri 05, 2021 2:56 pm
Posts: 128
Location: Brookline MA
Hmm, yeah the more I learn about synchronous motors, the more I realize they are amazing and you don't change their frequency that easily (in particular compared to the Technics-type that have potentiometers changing their speed)... I'm amazed by those technologies...

Anyway, this finding, added to the fact that if I change the motor for a 120V 60Hz I'll get into issues of feeding the amplifier enough volts, make it a sort of conundrum that is not a particularly attractive for a basic quality, non-audiophile device.

But what's more important even, I talked with the seller again and he's thinking he'll get emotional value for it, and emotions are too expensive for me to have a little fun with a funky device!

Thanks for the insight guys, that was a bad idea!


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 Post subject: Re: Changing motor or power supply on a Russian turntable
PostPosted: Jan Wed 25, 2023 8:22 pm 
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Joined: Jan Thu 01, 1970 12:00 am
Posts: 5081
Location: Boston, MA
If you do decide to go ahead with this, the easiest way to power it is to get a small 12VDC to 220V/50Hz inverter from Amazon UK or Amazon Germany, and run it from a small 12V AGM battery. You might get some slight buzz in the sound but there may be a way to filter that out.

-David


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 Post subject: Re: Changing motor or power supply on a Russian turntable
PostPosted: Jan Fri 27, 2023 12:14 am 
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Joined: Sep Mon 16, 2013 1:42 am
Posts: 6140
Location: Tucson, Arizona U.S.A.
Quote:
Hmm, yeah the more I learn about synchronous motors

That's not likely to be a synchronous motor; they're too expensive for a low end product where the average customer wouldn't notice the difference anyway. It looks like a 4 pole induction motor. It's surprising that it has 4 poles; American products generally used the cheaper 2 pole motors. Perhaps they were surplus from something else. The only way to know for sure what type of motor it has is by examining the rotor.

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Who's that swimming in the punch bowl?
It's Walter Wart, the freaky frog!


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