This brings us back to the Sony problem. On many sets you can use standard transistors and other semiconductors, at least for test purposes, so it is usually worth a punt for a few quid to see if it fixes the set. But an expensive chain failure which necessitates the use of genuine parts (a typical sony scenario!) means that these sets are not often worth bothering with. In this case I had no idea of the set's history, for all I know the tube could have been wasted too - another reason not to put serious time and money into such an item.
It is ironic that latterday CRT 'supermarket sets' tend to have a better chance of getting fixed than some of those costing several times as much!
-B