Tri-Planar grounding question...

The two should be the same.

The shield does not go through the gimbled bearings. Inside the arm tube, the tube itself is the shield. So the arm ground is usually picked up somewhere near the base, probably very near where the wires transverse the gimbles.

Jeff, I think you got it right. The reason it is not a ground loop is that the only place the ground occurs is the shield of the cable. Without that connection to the arm, the arm would be floating and it would buzz like crazy!

This concept is common to nearly all tonearms BTW (including BSRs from the 1960s). Since the arm is a separate ground circuit from the cartridge wiring, it is also why tone arms are or can be a balanced source.

Dogpile, my setup is balanced, but the wiring is identical up to the box in the cable. The Black wire is the shield up to the box and connects to the tone arm ground itself. After the box, the black wire breaks out to its own connection, and ties to the ground pin of the preamp at its input.