the problem with your 150 will undoubtably be its age.
if you look at the first 4 digits on the serial number this will tell you when it was manufactured - year/month e.g 9602 - february '96.
the chances are the tubes are tired and have been overused.
unfortunately on that model there is no clock on the tubes, so you can never tell how many hours it has done.
you can always try the fine focus ( above the green tube just behind the cross bar). this may give you a little adjustment, but not much.
a great budget machine in its time, but unfortunately coming to the end of its useful life.
hope this is of some help