Have you also transferred your 9k of transferable standard rate band to him?
If so, then your net pay from 2,755 would be about 2,127
If not, then your net pay from 2,755 would be about 1,970
From a gross of 800 p.m. your net would be about 778 (not affected by the rate band issue).
That's assuming you have only your PAYE credit of 1,650 available to you, and the full amount of your USC bands.