A 115 is rather a fine machine and few would replace it with just any other straight stitcher (because of it's rotary hook and race, runs smoother and less prone to vibrations). You have to search quite a bit to find a 115, but 66 machines comes in plenty. It's rather a fine machine too though, with the drop-in bobbin case. If the machine in your table is in nice condition there's no need to replace it, at least not the same model. Just get a motor and light setup, you can even get an original Singer motor. These models were made to be converted.
The subnumbers on the early 66 machines indicate either treadle, hand crank or electrical motor. Later on it was given a stitch length lever with backtack, and I think that's the 66-18. By then hand cranks and treadles sold were few and far between, and I have only seen them with original motor and light setup.
The base on model 15, 66 and 201 are the same. I think it's the same on 115 and 101 too. The very early 66 might have different hinges in the back, the earliest I have seen have dated to 1920 or a few years before (it was introduced in 1900). I know some very early 15s have different hinges in the back of the base, but it's a much older model.
Last edited by Mickey2; 05-30-2017 at 06:42 AM.