A TRACON Controller reported their radar unexpectedly failed resulting in a loss of separation between two aircraft they were vectoring for approach. One of the aircraft on vectors flew below the MVA.

Narrative

Our secondary radar has been out for several weeks. Aircraft X was not ADSB equiped but they advised when they were level at 2;000 ft. Aircraft Y did have ADSB and I kept him at 3;000 ft. Aircraft X was on a downwind for the VOR [approach] to Runway 4. Aircraft Y was in the downwind for the visual to Runway 4. I had turned both aircraft to a 270 heading and they had around 7 or 8 miles of separation at that time plus altitude separation. Then our primary radar went out so I lost radar on Aircraft X. It then came back up and I radar identified them and then I cleared Aircraft Y for the Visual. I turned Aircraft X on a 310 heading and I then lost primary radar again. By that time the Aircraft Y was at 2400 ft. so I did not have non radar separation. I did call the Tower for visual but I had already lost the separation at that point. After looking at the Falcon [radar replay system] when I got off position I also noticed that when I originally lost primary radar with Aircraft X and had them turning to a 270 I lost 5 miles with our 3100 ft. MVA.We have been reporting our secondary radar being out for multiple weeks because almost all of our military aircraft do not have ADSB so it makes our jobs much more difficult. Then having our primary radar go out without warning caused an even larger problem. With properly working radar none of this would have been an issue.