Singer Model 221. This machine is a 221S, which indicates manufacture in Kilkare, Scotland.
If your machine is like image #1, you have a Singer Model 221, more commonly known as “Featherweight.”
Image #2 features the tension disk assembly, which can be the cause of upper tension challenges and poor stitches. If you can get the machine to me, we will access the 221 manual, and you/I/we can disassemble, inspect, clean, reassemble, adjust the tension unit.