This is the type I grew up with:
http://www.ebay.com/itm/Two-Vintage-...-/260887109668
Parents and grandparents both had several blankets using that type of control. Note the power plug. The absence of a large flared surface at the point the blades come through dates it to sometime prior to the mid 1970s; anything later would have a more modern plug. Also, a polarized plug almost definitely means 70s or later.