What to do with a TT2?

[surayne]

Thanks Shane and Guy, that's reassuring. I've been doing a bit of cosmetic work to the turntable (repainting the MDF plinth and polishing the veneer), and have just popped on the arm. Hope to have it up and running later today, I'll post my thoughts and some pics.

Interesting. It's pretty much the same as the Linn pulley, and I've never understood the logic behind it. It's not possible to get a flat belt to run centrally on a pulley without a crown. It just won't do it. When I was trying to work out the design of the original pulley, I had to pretty much guess the radius of the crown. All the information I could find (there was no internet in those days, remember) came from research done in Victorian times when factory and farm equipment was driven by flat belts, and it was all pretty vague. You don't need much of a crown and in theory the pulley edges aren't needed, but you have to have something. On the Linn-type pulley, the belt just treats the angle between the flat portion of the pulley and the conical part as a crown and runs on that, as shown perfectly in your second picture. (Brilliant photos, by the way!)
What I could never work out was which diameter to use to calculate the speed. In the end, I think we just tried reducing the diameter by degrees until we got it right.

As far as removing the ball from the bearing is concerned, I wouldn't bother. The ball is aclose fit in the bearing. If you take a new bearing with no oil in, the ball takes about 20 seconds to reach the bottom of the bearing. Introduce some oil, and the oil seals the minute gap around the ball almost perfectly. If you try to force the ball in under these circumstances, the air pressure will force the brass plug out of the bottom of the bearing.Iin the same way, it's almost impossible to remove the ball once there is oil in the beaing because air cannot get past the ball. The only way I've ever managed it is to push the ball and the plug out of the bottom together. Not recommended!

There shouldn't really be any need anyway. Cotton buds or a rolled-up soft clotth will be sufficient.

[AlfaGTV]

Why do you say that this is an extreme picture? The belt is riding in, essentially, the correct position.

The belt is normally (when running) riding a bit higher, with the lower part of the belt just touching the conical part of the pulley.

To be honest, I don't see how one is easier to adjust than the other? A strobe is required for the first, but at least it directly adjusts the speed (by adjusting the effective diameter that the belt sees).

You misunderstood, the speed of the turntables is quite correct, with the modern one steady at 33.3-33.5rpm and the older one a little bit higher and with more variations, typically between 33.5-33.9rpm. Checked with a cheapie from fleabay, but accurate enough imo.
The issue is that i want the drive belt to keep its position on the pulleys to make it easier to adjust suspension. And the crown on the pulley makes the belt self-center up to a certain degree.

No, there is no inherent disadvantage to a crowned drive pulley.

Let me try and explain my theory:
When the belt makes contact with the crowned pulley, the belt will stretch more in belt center, than on the edges based on the different diameters. No rubber belt is 100% homogenous and this will cause variations in resistance and spring force. Thus introducing more variations in speed than with the straight pulley where the diameter ideally shuld be the same for all parts of the belt?

Both the drive pulleys you show are effectively the same thing, crowned pulleys. The only difference is that the first allows the profile of the crown to be altered by tilting the vertical axis of the motor relative to the plane of the belt. The second assumes that this mechanical adjustment will be made electrically. Neither pulley solution is better, or worse, than the other in mechanical terms as both achieve belt centring my the same method, and a crowned pulley is the best solution.

I really dont understand what you mean here? Are you referring to adjusting the speed?

However, if everything is accurately machined to a sufficiently high tolerance and the belt produced similarly, belt wander should not be an issue even on a straight sided pulley (unfortunately this is not always true, even for many 'quality' turntables).

Nah, you're right. This is mostly a non-issue, but i would like to eliminate any potential sources of concern.

and thanks for your input!
/Mike

[DSJR]

Once set up, just run the thing for a few hours, which should sort the belt out (possibly stored for decades folded in some way?)

Now watch the price of old TT2's go through the roof!

[YNWaN]

The belt is normally (when running) riding a bit higher, with the lower part of the belt just touching the conical part of the pulley.

Where it specifically rides depends on the exact diameter of the inner platter. There's no need to post a 'rolling your eyes' icon , I know what I'm writing about.

You misunderstood, the speed of the turntables is quite correct, with the modern one steady at 33.3-33.5rpm and the older one a little bit higher and with more variations, typically between 33.5-33.9rpm. Checked with a cheapie from fleabay, but accurate enough imo.
The issue is that i want the drive belt to keep its position on the pulleys to make it easier to adjust suspension. And the crown on the pulley makes the belt self-center up to a certain degree.

Well, perhaps I do misunderstand you. Both types of pulley are essentially crowned so both should have a self centering quality (assuming the belt is positioned correctly).

Let me try and explain my theory:
When the belt makes contact with the crowned pulley, the belt will stretch more in belt center, than on the edges based on the different diameters. No rubber belt is 100% homogenous and this will cause variations in resistance and spring force. Thus introducing more variations in speed than with the straight pulley where the diameter ideally shuld be the same for all parts of the belt?

Well, it's a theory; however, it's not one I have found to be an issue in practice. Absolute concentricity of the drive pulley and the drive shaft are much bigger issues.

I really dont understand what you mean here? Are you referring to adjusting the speed?

Yes.

[AlfaGTV]

Where it specifically rides depends on the exact diameter of the inner platter. There's no need to post a 'rolling your eyes' icon , I know what I'm writing about.

Apologies, I was meaning to say that i dont know exactly how to express myself. Not intended to your post in any way!

But you are really saying that the belt position is more or less correct in this image:

It is supposed to ride partly on the conical section?

Regards
/Mike

[YNWaN]

That's OK.

Yes, That's correct, precisely so. The belt is intended to ride on both surfaces - the transition between the two acting as the crown that helps belt stability. As the motor (and therefore the pulley) is tilted the belt runs more, or less, on the vertical element of the pulley; this effectively alters the diameter of the pulley and so changes the gearing and speed of the platter. If the belt runs entirely (or almost entirely) on the vertical section of the pulley the pulley is either slightly too small or the inner platter is slightly too large (relative to each other) - belt tension may also be too high, as may be bearing drag or friction. Ideally, the belt isn't intended to run pretty much as your picture shows.

[surayne]

If it becomes necessary to replace the motor, would the current 24V Rega DC motor be an option? As I understand it the early Regas used the same AC synchronous motor as the TT2, the new motor is meant to be backward-compatible. This would potentially give the option of adding the TTPSU for speed control... Just a thought!

[surayne]

Well, here she is after a hard day's work...

Slideshow

[Macca]

Well, here she is after a hard day's work...

Slideshow

Brilliant! Looks brand new.

[shane]

Well, here she is after a hard day's work...

Slideshow

Looks a million dollars!

With respect, isn't 'critics corner' the section of the forum in which to raise such issues?

Why? The question is relevant to this thread. Why make everyone fart around looking for the answer somewhere else?

I can't think of any reason why it shouldn't work, and I'd be really interested to hear if it was worthwhile.