Need advice on RAE-84 motor

[gramophone-georg]

I have an RAE-84 I am trying to defeat some issues on. First on the list is that the turntable is too fast- like about 10 RPM too fast! According to the service info I have there may be a governor on this motor but i sure am not seeing it. Of course, I'm no expert on this machine. Can someone point me in the right direction here? I picked up a voltage reducing rheostat off Amazon that plugs into the power source, then the machine plugs into the rheostat box. Reducing the voltage allows me to control turntable speed but takes the annoying little buzz in the amp and puts it on steroids.

[pallophotophone]

Hi George,

I'd highly recommend that you discontinue the use of the the rheostat as it will raise first class hades with the electronics- not to mention the mercury vapor rectifiers that this set uses.
If your phonograph uses the same motor that my RAE- 79 uses, the motor isn't governor controlled. The line frequency determines the speed. It is called a synchronous motor.
The speed reduction for 33 ⅓ rpm is accomplished through planetary gearing. If your motor was designed for 50 cycle service, it would run too fast on 60 cycle. If the electronics was designed to run on 50 cycles, it will run happily on 60 cycles if everything is right with it.
After giving this a little more thought, your motor may not have the prerequisite torque to operate the record changer at a reduced line voltage.
Take a look around inside the case and see if there is a paper label with the operating parameters on it. If its 50 cycles not 60 cycles- that would confirm it.

I hope this helps !!

[gramophone-georg]

Hi George,

I'd highly recommend that you discontinue the use of the the rheostat as it will raise first class hades with the electronics- not to mention the mercury vapor rectifiers that this set uses.
If your phonograph uses the same motor that my RAE- 79 uses, the motor isn't governor controlled. The line frequency determines the speed. It is called a synchronous motor.
The speed reduction for 33 ⅓ rpm is accomplished through planetary gearing. If your motor was designed for 50 cycle service, it would run too fast on 60 cycle. If the electronics was designed to run on 50 cycles, it will run happily on 60 cycles if everything is right with it.
After giving this a little more thought, your motor may not have the prerequisite torque to operate the record changer at a reduced line voltage.
Take a look around inside the case and see if there is a paper label with the operating parameters on it. If its 50 cycles not 60 cycles- that would confirm it.

I hope this helps !!

Only used the rheostat for a few minutes as I figured the interference through the amp and speaker couldn't be healthy.
Sorry, but no paper tag in the cabinet- drat. The service notes say this can be rated for 50 OR 60 Hz, so you may be correct about the motor being 50 as 60 would speed it up. The changer also has issues so did not try cycling it. I need to readjust all the specs on it as it sure is finicky.

My other problem is pretty discernable "wow", even at 78. Winds up that the trip gear on the shaft that the TT 33/78 gear changer sits on is loose on the shaft and bobs. I was able to get some of this out by putting a thin shim under the gear to remove some of the bob when the set screw is tightened, but it seems to fix it right I'll need another gear or I'll need to try a sleeve in this one. The turntable had quite the "wave" in it before.

Thanks for the idea. Seems I may need to put a known guaranteed 60hz phono motor on my parts list.

[pallophotophone]

You might be able to get your motor rewound to work on 60 hz. A good motor shop could advise. If the field form is the same for 50 as for 60, it might be workable.
Obviously you'd need to confirm the condition of the armature bearings, worm and turntable drive gear are all 100% before going down that road. The rewind won't be inexpensive, but it might be a way out.

[Marco Gilardetti]

If the motor is really syncronous, I think that rewinding the coils would be useless by definition, as the rotational speed is given only by the number of poles (and frequency, of course).

[pallophotophone]

That's a good point- I was only considering the number of poles in the equation.
If it wasn't synchronous, it would just run free. That's why many types of Victor phonograph electrical motors use a mechanical governor and why this one doesn't.

[JerryVan]

How exactly does the motor drive the turntable? Direct drive? Belt drive? Friction wheels? Maybe the shaft diameter of the drive motor can be reduced to change the drive ratio.

[pallophotophone]

It's direct drive via a worm that is part of the motor shaft and spur gear that is directly coupled to the turntable spindle.
Probably very very expensive to manufacture a new worm and spur gear. And that would not change the rotational speed of the motor. Only the line frequency that drives the motor would change that.

[JerryVan]

Probably very very expensive to manufacture a new worm and spur gear. And that would not change the rotational speed of the motor. Only the line frequency that drives the motor would change that.

Yes, it would be very expensive, if you could even find someone to do it. But, if designed correctly, it would change the speed of the turntable by changing the helix angle of the worm. In any case, not practical for this application.

Maybe some form of a VFD, (variable frequency drive), could help, but I'm not smart enough to suggest anything along those lines.

You might try using your rheostat control on the motor only, and not on the whole unit.

UPDATE: I posed the question of a VFD on another forum I haunt. Let's see what the brainiacs there say!

[pallophotophone]

I've done it before with an audio amplifier having a 70 volt output and a frequency stable audio oscillator to drive a motor used in a wire recorder. Not bragging - just stating a fact.

The rheostat will reduce the speed, but also the torque so it may not run the changer.