All tubes look pretty much the same from the front. You'll need the tube number. That's inside on the back of the tube.
Hate to say it, but if it's ~10 years old, it is probably the smaller neck version, compatible with a B&K CR-31 adapter. You want one that's compatible with a CR-23.
Don't toss it though...there are plenty of monitors that can use that kind of tube.
But the most important thing is finding that tube number. If you don't want to crack it open, maybe you can look in thru the air vents.