Anyway to Slow Down my Pabst Motor

[thebes]

Recently acquired an old Empire 398 which comes with the famous Pabst motor. It runs to fast even after the proper belt adjustments. Ordered up a new belt from Alex Atleier which are the ones everyone online says are the correct belt. Still too fast.

This is an AS motor and with 3 poles and was factory built to run deadon at correct speed. I've removed it and lubrication is still present and the bottom motor bearing if in fine shape and no wobbles or anything in the shaft that I can see. Runs very quiet and motor mounting isolation grommets are in fine shape.

There are two capacitors, in the turntable power supply, a .02 Z ceramic capacitor and a 4uf 230 volt can capacitor. That's it. No circuit boards, resistors etc.

I found this online:

"The Papst motor is an Eddy Current
motor. The relative contributors to the Papst motors' speed regulation
are: mains frequency (97%), torque load (2-3%) and drive voltage (<1%). Generally, 3-phase electrical power
is used in industrial settings, not residential, which is single-phase. To get
the motor to run on household current, a capacitor is connected across two of
the three leads and "fakes" the motor into working.

Another important detail is this; the
rotating part is the outer casing, while the stator, the part with the
windings, remains fixed. This design results in a relatively high moment
of inertia at the rotor, giving a flywheel effect. When turned by hand, the
turn of the rotor exhibits no magnetic cogging as does a more traditional
synchronous motor such as those found on Thorens' belt drive models. This
is an interesting turntable motor."

I've tried to slow things down by using a variac, figuring house main voltages are higher these days, but no joy. I'm wondering if either of the caps could be the problem and since the ceramic .02 Z cap is the one across two of the 3 leads. Should I simply replace these or could I vary the size of this cap to achieve a lower speed, or perhaps insert a resistor?

The speed is readily apparant in the music and at it's best setting is still much faster than my Rega P3 which is notorious for runing fast.

[JJkizak]

If this is a 3 phase motor how can you get it to run with 1 phase 120 volt input ? You would need 220 volt single phase input (2 phase) for the capacitors to shift for the third phase.

JJK

[jacksonbart]

This poster may actually spead up your Pabst motor

[thebes]

If this is a 3 phase motor how can you get it to run with 1 phase 120 volt input ? You would need 220 volt single phase input (2 phase) for the capacitors to shift for the third phase.

JJK

Durn if I know.

Here's the breakdown though. One of the 3 wires coming from the motor goes directly to one side of the outlet plug. One goes to one side of the 4uf can. The last one goes to one side of the ceramic cap. The other side of the outlet plug goes to the other side of the ceramic cap. There's a few other wires for ground and to the pilot light and on/off switch, but that's essentially the circuit as I see it.

[JJkizak]

I would try replacing the "Can" first. Design life is about 20 years max.

JJK

[WMcD]

I don't know much about this. But why be bothered with ignorance.

Is there any chance this was a turntable meant for European line frequencies? Maybe the seller unloaded it because of such an issue.

Take a look at http://www.wiringmanual.com/drives002.html

You'd think that asynchronous motors are not synced to the a.c. line frequency at all. It seems that it does "slip" somewhat.

But one of the equations indicates that the speed is affected by the line frequency and the number of pole pairs within the motor. Note also that the examplar spec plate on a motor calls out a line freq.

This makes me think that a given motor must be constructed (with internal pole pairs) to reach a given speed, depending on the a.c. line freq.

Now you know what I know.

Wm Gil McD

[djk]

Sounds like you need a 60hz pulley.

If it's only off a fraction of 1% or so, you can polish the pulley with some emery cloth to slow it down.

[thebes]

Well it's a 60hz motor and I'm using a 60hz stobe to time it (actually two different strobes) and I thought about grinding down the pulley a bit but I'm afraid the speeds a bit to high for that to effect it. The knob adjustment for the belt tension is basically a pitch control and I've read online that it only controls either 1/2 or 1% of the speed and that's not enough.

Yeah I'm thinking the can, but since I don't undertand why you need cans to control a motor it just a shot in the dark for me.

I do have two 2uf 600v rated metal/foil crossover type cans. Maybe I can wire them together as an experiment. Question is do I wire one can to the other and then to the motor wire or wire both cans at the same time to the motor wire? Don't want to blow up a motor that routinely sells for $200 on the bay.

[thebes]

Thanks Gil for the info. I do believe you can vary the speed by controlling the frequency. There was a guy on Audio Asylum that made a few Pabst controllers for a short while and I saw a picture of it. It was complicated and had to exactly regulate the frequency of all 3 poles and had 3 seperate gizmos that looked sorta like inductors plus a lot of caps,resistors and a power supply, maybe even a diode or two. (I think I'm saying this right but don't bank on it.)

[thebes]

I've also read that you can use a silk thread in lieu of a belt. Anybody know what kind of or thickness of silk thread and do you just tie it into a knot?

[djk]

I would just buy a junker Thorens 125 or BIC 980/1000 and yank out the oscillator module.

[WMcD]

I found this http://electojects.com/motors/tesla-induction-motors-5.htm.

I don't know if you have that starter switch built into something on your TT. And it doesn't answer the speed issue.

Wm McD

[LarryC]

Marty, you've got mail.

[thebes]

Gil, interesting article and based on it I decided to swap out the ceramic cap first. No change. Then thanks to an email from BEC strung two 2uf caps together, wired them up and tried it out. No change in speed so it's not the caps.

I have managed to slow it down a little by using 90 weight oil in the bearing hole and using some chalk on the belt but it's still too fast.

I've got some sewing thread around maybe I'll give that a try.

DJ sounds like a great suggestion. Do you think the motor pc board they are referring to on this site is the part that I need? Also I presume you are suggesting those specific turntables because they used 3 phase motors.

http://turntableexperts.com/html/bic.html

[Marvel]

Put these under the feet... if this doesn't work, nothing will.

[thebes]

Well problem solved. It's the belt. Too thick. I tried some dental floss and with that on it runs too slow. Wish I had tried that first.

I studied this issue carefully before I ordered the new belt and ordered from Alex Alteier which supposedly supplies the only accurate belts for this table. Paid $31.50 when these things sell routinely on ebay for $12. Guess the collective online audio gurus talking about these belts were collectively wrong.

I'll try some 6lb. fishing line next and contact the belt people to see if they have anything else that might do the trick.

What a Pita and thanks for all your help.

[JJkizak]

Don't feel bad. There are correct belts and there are incorrect cheapo belts.

JJK

[djk]

"Do you think the motor pc board they are referring to on this site is the part that I need?"

Yes.

" Also I presume you are suggesting those specific turntables because they used 3 phase motors."

You don't need 3-phase, the existing cap is all the TT needs to run on single-phase. The oscillator module just varies the frequency to vary motor speed.

[bliss53]

Well problem solved. It's the belt. Too thick. I tried some dental floss and with that on it runs too slow.

Could the speed problem be related to traction (slipage)? Have you tried a little talc on the floss or the belt?

[thebes]

Don't feel bad. There are correct belts and there are incorrect cheapo belts.

JJK

That's what's frosting me about this whole thing. These are supposed to be the only belts you should even contemplate buying for the Empires.

I emailed the company and will see what they say before deciding weather to buy the oscillator, and for that I do thank you DJ.

Bliss, I did use some talc and it's not belt slippage. With the dental floss, it's already waxed and grips well, but these are tables are not set up for string belts with attendant grooves in the platter and bearing. You can't fine tune them and they won't last long. Went to Michael's, the craft store, yesterday and tried some various strings but no joy. Some fringe I saw would work well but no way to evenly connect it without overlapping, thus a thump, thump, thump as the connected ends come around.

Besides if I started putting fringe on my turntable people would start to talk. (Why that man's nothing but a Nancy!)