Maple platform under turntable, How thick?

As thick as a tombstone.

Whatever thickness you can get, I would suggest buying a bunch of squash balls and putting them underneath. It's kind of like a cheap man's Ginko cloud, but with a maple flavor to it. You'll probably need at least 8-9 balls for the weight.

One of the better things I did for my TT.

Enjoy,
Bob

Anyone used Polycrystal amp stand under turntable or tape deck?

All right. Thank you everyone. I will try Mapleshade 4" with their footers and will have brass cones for comparizon.
Over $200 for a piece of wood, oh, beg your pardon, air-dried hand-selected Amish craftsmen made piece of wood.

Under my Teres 320 I've been using a three-inch thick, two-foot square maple from Tony's Woodshop (look under multimedia storage). Its not Amish, but a few yrs ago it was ~$75 w/ shipping. The maple block sits on doubled-up corrugated-rubber-and-cork pad thingies like Mapleshade sells, but got them much cheaper, example here: http://atlantavibrationpads.com/rubberandcorkpads.aspx