Cor, the following could shed some light to establish if it is the tube or not (this works with RF models but not sure with the older one, but worthwhile to give a try).
!! If you're confident working inside a tv it's a small thing but if not don't bother as you may do more damage to yourself and the tv !! (but ask someone to do this for you who is able to).
-Take off the video output board from (the back of) the picture tube (leave it connected to the rest of the tv).
Now try to switch on the tv, carefully listen if it does the degauss sound and the ''crackle'' of the HT coming up, also it may look like it's working when you look at the display (showing TV-1 and you'll be able to change channels).
Don't leave it on for long time, it only needs 10-20 seconds to do this test (it might damage the tv if you leave it on, not sure...it might not but just to be safe).
If it acts as above (switches on, HT present) the problem will be the tube.
If there's no change compared to your earlier description of the problem, there's something else wrong.
Good luck :).