Turntable motor spindle is slightly bent...


2002-01-31 7:17 pm
and introduces a very, very slight wobble to the pulley. The bend is at the extreme end where the pulley is. I'm experiencing slight speed instability but don't know if it's due to the wobble or due to another problem, i.e. in the speed controller (sometimes the speed is dead-on right). Belt is new from manufacturer.

I want to "fix" the spindle first so that I can rule that out first.

There are no analog shops anywhere near (350 miles) where I live. Do I dare try to simply, and gently, bend the shaft with a pair of pliers or would I be better off taking the motor to a machine shop? Or am I SOL? Just wondering if any of you have had any experiences with bent motor shafts.

Any and all suggestions (well, most) are appreciated.

AFAIR, you own an Oracle Delphi with a Pabst GS3809 as motor, right?
If so, bad luck, the motor has been discontinued for long.

Check whether the shaft is really bent or whether the pulley sits tilted on the shaft (particularly if the pulley is clamped by a single radially orieneted screw). I had this problem myself and was surprised how much pulley tilt is neccessary to become audible as flutter (of course, it fogs the sound way before flutter is occurring).

Otherwise it could be the switch determining whether the platter speed is 33 or 45. This switch is in series with the trimpot adjusting the motor's speed. If now the switch increases it's contact resistance, this spoils the speed, allthemore as this resistance increase is arbitrary and fluctuating, can vary from one occasion to another. If you platter has better speed constancy at either 45 or 33, it is very probable this switch is the daemon. Replace the switch and see whether your problem fades.

A bent shaft is very hard to repair, it is to be considered as a final damage commercially.
You would have to have a precision mechanic grind the shaft to a smaller diameter and then have him make a new pulley for that diameter. But the emory coming off the grinding disc must not come by any means into the motor's bearing. Tricky, very tricky.
Forgetabout bending it back, bending metal is alchemy. Instead of un-bending, you are very likely to add a bend to the bend. Moreover, you put way too much load on the bearing surface by bending it back.

You could try to buy a new sample from J.Räke/Transrotor (Germany), TMK he bought the rest when the motor was discontinued. But he will charge over US$300 and you will probably have to convince him you own a Gyrodeck or Transrotor TT.
Or you could try to talk me pout of my last backup sample; i decided to build a new motor unit and won't need it anymore ... but i want to have almost the same money as Räke, i don't wanna loose money on it and those motors go even higher as NOS on ebay.

Another suggestion: you build yourself a new motor unit using a different motor and i tell you all secrets you need to know about this.
The motor unit i have am currently planning for my own TT is not a replacement, it is an improvement. I use a maxon DC motor (expensivish but easily avaiable) and a simple voltage regulator as power supply. I let this motor sit on a sled and have a littel weight pulling the motor away form the platter spindle in order to have a well defined belt tension. And then i use a magnetic tape as belt.
And have 16, 33, 45, 78, 120 if desired.

How does that sound?

One thing, at our local surplus store, i bought today 5 samples of a maxon motor very well suited for the job for less than $10 apiece. Unfortunaltely it has a gear wheel on its shaft. But i am sure i will get it off w/o damage. If you decide to go that path, i would pick up another 5 pieces for you and mail them to you and you send me the money via PayPal. But ... make a fast descision, they won't be there for long.


2002-01-31 7:17 pm
Hi Bernhard,

As you have suggested, I did wonder if the pulley is simply on the shaft at a slight angle (a single set screw is NOT a good idea). I'll be attempting to remove the pulley this weekend to take a closer look

And as you also suggested, I had wondered if there was something wrong in the speed control. I was just afraid to voice this as I'm trying to address the simple things first.

My inclination is that there *is* some sort of back and forth with the speed control, as sometimes it is dead on right. Only sometimes does the speed variation show up. One time I had accidentally pushed the speed control for the 45 setting, and when pushing it again, the table slowed, but not down to anything near to 33, thus a faulty switch may well be the culprit.

Nice to have you confirm my neophyte inclinations. I'll let you know what I find out.

As always, your kindness is greatly appreciated.


2002-01-07 6:02 pm
Hello Bernhard,

Could you please tell me the model number of the Maxon motor? I have wanted to experiment with DC motors on my TT's for some time now, and the Maxons were suggested, but never a model number, and the local agent was not very helpful. I know their quality and low vibration from using the higer powered versions in a robotics project some years ago.

Alternatively, if Lonestar does does not want your extras I would be interested in 3 or 4 of them.

Lonestar and Brett,

there should be enough maxons for both of you. I meanwhile found the motor in question is industrial surplus (not in the catalogue) but i spotted supply voltage, wattage, torque, speed from the winding code (949).
It is a 42Volts type which is good. 9V for 33.3 rpm are easier to regulate than 4.5 or 2 Volts.

Consider the motor is used way below it's nominal speed of about 6000 rpm. I do not recommend an excentricity frequency of >20Hz which for 33.3 limits speed to 1200, better below. The motor still can cover 120 rpm which is the highest oddball speed reported from the shellac realm.

I come back with results as far as the gear wheel pulley removal is concerned, you tell me you order and i mail them at cost, ok?

do you know other usefull things about Oracle Delphi motors? I own an MKIII and had a look at the motor a while ago cause oracle changed it when going from MKIII to MKIV. I would like to improve the motorsteering but haven´t got a clue how it functions (no diagram). I´ve tried a few different transformers and they made a difference in sound (although none was better as the standard one).



2002-01-31 7:17 pm

Checked the spindle. If it IS bent, it's only a small fraction of a mm. The wobble is indeed from the pulley and it is more visually noticeable due to the flat upper and lower edges. The barrel shape portion that the belt rides on is staying quite true. So Bernhard, you are most likely correct, the pulley isn't the cause of the speed variation.

The speed control is indeed the problem--most likely the switch, as you suggested. Last evening, when switching between speeds, the 45 rpm setting completely went crazy, actually running slower than the 33 rpm setting. No amount of trim-pot adjusting could overcome this.

I'll check out the switch as soon as possible and get back to you re the Maxon motor. From our prior conversations elsewhere, I believe that the best performance to be had from a new speed controller and battery ps. I just have the desire to retain the Pabst if at all possible.

I'll keep you posted.


2008-02-25 6:23 pm
Oracle - Which Model

Hello, I have 2 Oracle tables.

One is a Mk V w a Turbo psu and I also have a spare Turbo psu.

Plus, I have another Oracle which was sold to me as a MkII. It has the black square motor. Oracle on the phone says it is a Mk One however

Q: Which one is it?

And, can I use the spare Turbo psu with this square black motor? How to interface the connectors, being a 'pin' type vs a 'looks like a DIN style type (on the Turbo) ?

Thanks, new here.