My setup is a T4 with the SG200 and the 2 Japanese Sun Tiger Wheels 800 and 4000 grit.
I am successful in getting most my gouges, chisels and plane blades having sharp. I use the SVS 36 for all since is the only relevant jig I have.
However I came across 2 blades (both of them vintage blades bought in Germany) that I have failed (using the svs36). The burr was extremely hard to get rid of and when I did succeed to bring it to a really good cutting shape (not hair popping sharp as I like), after very few passes on a soft fur I see the edge getting damaged A LOT.
Any ideas? I would blame the steel but I am not that experienced and confident to do so.
It sounds to me like the old irons have lost their temper. If the steel is too soft then the burr will be difficult to remove.