It looks like a 106 variant of some description. The serial dates it to around 1937/1938 but I wouldn't expect to see a balance without screws from that date.
I haven't seen all of the 106 variants but I have never seen one with a plain balance, nor that regulator and the balance cock is a slightly different shape from the ones I have seen.
Does it have a seconds sub-dial or is it a central seconds movement? - they made both in the 106.