if you rotate a tube you don't touch the yoke,that should remain at factory setting.you should put your yoke back to its original position,if you still have purity issues then first make sure the tube is degaussed then if you still have a problem you need to get a grid test pattern on your tube and then starting with green adjust the purity rings one by one(warning this is a big,time consuming job not to be taken lightly and remember you have to loosen the lock ring at the base first)