Installing cartr.:slide it all the way to front?

Welcome back Overhang,

First of all, nice new rig! It should play some great music.

If you view the tonearm from directly above and swing the arm back and forth, you can visually imagine the exact point around which it swings. That is the pivot point, the only spot on the arm that DOESN'T move when you swing it.

There's no obvious visual spot at the pivot point on an RB600 so here's what I do: stick a small piece of Scotch tape on top of the arm tube, above the pivot point you just identified. Mark a dot above the pivot point with a pen. Swing the arm a couple of times to confirm the dot isn't moving. If the dot moves, change the position of the tape and try again. When the dot remains stationary you've marked the pivot point. Voila!

Now measure the distance from that point to the center of the TT spindle, in mm. Close counts, + or - 1mm is good enough. Let us know that dimension and we'll go to step 2.

Re: spacers
Once the Shelter is securely mounted and can drop it onto a record you can tell whether you need spacer(s) or not. Shelters typically like to have the cartridge body VERY SLIGHTLY tail-down. Use whatever spacers you need to achieve that orientation.

Thanks Doug.The distance is 216-218 mm.

Raul,
I must have been sleepy. Of course an SME IV/V changes mounting distance when moved on its rack.

In plain 2-D geometry the SME rack is a straight line segment. The TT spindle is a point. Any object moving along a straight line MUST change its distance from a fixed point.

The only path an object can travel without changing distance from a fixed point is a circle with said point at its center.

The SME rack is not a circle or any portion of one. If it were, moving the arm would not alter its relation to the platter or the LP. Such a mechanism would serve no purpose, the arm would literally be going in circles!

Overhang,

AHA! Progress.

It appears your Gyro was used with some arm that needed a shorter mounting distance than a Rega. Fortunately, the Gyro's armboad is adjustable. I don't know the details but there are one or more screws you loosen, after which the mounting plate spins. You'll note the arm mounting hole is offset, so spinning the mounting plate changes the arm's distance from the spindle.

Try to make your spindle-pivot dimension 219-220mm. That's the optimum for a Rega to achieve 2-point Baerwald alignment, which is widely considered the best scheme.

If you can do that, visit www.TurnTableBasics.com and buy their $20 mirrored alignment protractor. The TTB is probably the most accurate protractor short of a $150 WallyTractor. You'll be all set.

Doug

P.S. Don't bother trying to align a cartridge using your Rega protractor with the arm at 216-218mm. It won't be possible. That protractor assumes 223mm. If you don't want to buy the TTB protractor and just want to use the Rega one, you'll have to swivel the arm's pivot point all the way out to 223mm.

DougDeacon,

A way one might keep optimal Rega mount distance and align ala Baerwald may be to relegate any protractor that constrains to the dustbin. I suspect that the one size fits all approach to some protractors that are not arm specific might have their own proximation pitfalls built in.
The two null points for Regas are 60mm and 115mm from center spindle. With some oak tag and a compass, couldn’t you just make up your own? Using a little plane geometry, you can even come up with “squaring off” alignment boxes. Just a thought in the direction that I’d consider before changing the arm’s throw.