I've made a bloody mess!

[andy]

You almost certainly have one or more bad electrolytic caps in the vertical section. They can dry out over time, even if not used. The best way to find them is with an ESR meter which measure the caps internal resistance. The other way is to temporarily sub a new cap for each cap until you find the bad one. There's also a chance of some off value resistors in the vertical section. Since the set was never used, I would be about 99% sure a tube isn't the problem. If you don't have a schematic of the set, I would strongly suggest getting one so you can quicly ID the caps used in the vertical circuit. They aren't always all located near the vertical osc and output tubes.