I am in progress of installing 3/4 solid oak over a 3/4 plywood subfloor which is attached to my concrete slab. There are a few spots where the wood floor will meet an existing tile floor (the tile is set in thinset directly on the slab).

The reduction in floor height to the tile is almost 1 & 1/2 inches. The thickest reducer I can find is only 3/4. Has anyone delt with this problem before? I would prefer to buy the appropriate reducer but can fabricate if necessary. Just looking for the simplest solution. Any advice is appreciated.

What is your location.

Simplest solution would be to scab on a piece of the flooring, ripped to the thickness of the exposed plywood edge and install the 3/4 inch reducer on top, meeting up to the edge of the piece you put on. This gives you all exposed wood as pre-finished (assuming of course you are installing a pre-finished floor. If this facer piece projects too far into the tiled area, you can further rip it to a thinner piece, sort of like a veneer. Make sense? Clear as mud to me, lol.

I don't know that I fully understand what you mean. It sounds like you are suggesting that I only reduce 3/4 of an inch? I was hoping to reduce the entire 1 1/2" with one solid piece. Also, the floor is unfinished.

Well if you are planning the full reduction you woll need a fairly wide space so that it doesn't end up looking like a ramp. Say about 4 inches will give you a gentle enough slope. Since you are working with unfinished floor, just get yourself a chunk of 8/4 oak 4 inches wide, and appropriate length from the lumberyard and fabricate your threshold from that. There are other more complex ways of fabrication, but that would be the simplest.