The only way to get a decent picture (from a computer or game console) out of an old CRT monitor is to use RGB connectors. A CRT TV is a fixed-sync RGB monitor, even if it does not have a VGA port. Most SCART connectors have RGB input (usually only one, and they are usually labeled "RGB"). Sometimes the CRT has coaxial RGB input, so you need to check the backside of your TV.
Using RCA connectors will give extremely bad picture (think VHS quality), but I suppose RGB adapters are getting quite hard to come by these days (they used to be very common during the CRT era). There seems to be plenty of cheap adapters on eBay though.