contina: Primafon - 50 vs. 60 Hz turntable speed

Radio friends,

I'm working on an interesting Italian console radio/phono.  The unit appears to be a combination of a Vertola radio (modified, perhaps homebrew) and a Contina turntable identical to that shown for this model.

The instruction page (viewable here on the Primafon model page) mentions that the turntable has an induction motor with selectable voltage ranges 110-120, 140-160, and 210-220 VAC.  It also indicates 40-60 Hz, selectable ("40-60 Hz umshcaltbar").

I have found a typical "wheel" type voltage selector on the unit, but I'm having trouble understanding how the AC line frequency could be adjustable.  Induction motors tend to run at a single speed tied to the line frequency, and this one appears to be no different.

Does anyone know what they meant by "40-60 Hz umchaltbar"?  Is there in fact a way to make this run the correct speed on 60 Hz?

As it currently stands, it runs too fast, as one would expect when running a turntable designed for 50 Hz on a 60 Hz line.

On a related note, does anyone know of a source for replacement rubber tires for the idler and turret on this turntable?  The originals are still working to some extent, but new rubber would be much better.

Thanks,

Tom

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The spindle end must be replaceable. That's the only way to change speed vs frequency.

 

Maybe like how when you buy a gas appliance it comes with jets for town gas or bottle gas :-)

 

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As Michael says, rubber-wheel or belt drive turntables with AC motors usually used different motor-pulleys for 50Hz or 60Hz. This "pulley" is really the motor shaft (or extension) with several diameter steps.

In a 33/45 machine, it is possible to have four steps. Two give 33/45 at 50Hz, two give 33/45 at 60Hz. A 2-way user knob selects 33 or 45. For 50/60 your service shop moves a spacer so the rubber wheel will hit on steps 2&4 instead of 1&3.

But 16/33/45/78 at 40-50-60 is 12 steps which is unlikely.

An alternate scheme is to taper each step and adjust the rubber wheel up or down to hit at the right diameter. Simple mechanical +/-3 semi-tone pitch adjusters worked this way. They were never at the right pitch unless adjusted daily.

Many-many phonos had to change motor-pulley. If shipped to 50Hz land they were built with the -50 pulley; to 60-Hz land with the -60 pulley. Since most phonos did not move between power grids, nobody cared. When people moved from UK to US we sometimes tried to get 60Hz pulleys to convert them. IIRC Dual often had the -60 part in stock, most other brands were unresponsive or never had the part.

Take some clear pictures of the motor shaft and rubber wheel. Documentation is always good, and maybe the speed-set method will reveal itself.

For reference: the motor is surely under 10 Watts. A 10 Watt 8-ohm audio amplifier into a 6VAC:120/240VAC transformer will spin it 40Hz-100+Hz via an audio oscillator. I have done this to hot-rod a 33/45 turntable to 78 RPM (104Hz). It would be a major project to build-in such a supply. But it is a really cute machine and it would be nice if it played at the right speed. 

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I've talked with the owner of the phonograph, and he as OK'ed me to go ahead and machine the motor spindle down.  This of course will not be reversible, but the odds are that this unit will be in this country for many years to come.

This turntable has a turret (instead of a simple idler), so replacing the turret may well have been the method that was originally intented.  Replacement of one part would then effect a common conversion for all speeds.  However, it's not easy to make a new turret; while machining the spindle down is something I can do pretty easily.

Tom

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