[Arran]

Before you write off the tubes it would be a good idea to check the voltage of your tube tester under load, some tube testers will not put out enough current to power 1.5 volt or 2.5 volt AC tubes on the 2.5 volt setting, I've had to set my tube tester to 3 volts or more with 2.5 volt tubes, and 2-2.5 volts for #26 tubes, and play with the rhestat, and a volt meter, to get the correct filament voltage at the correct current.One sure way to tell is by the colour of the filaments/heaters, they should be a bright orange colour, not dark orange. Another thing to watch are the solder joints on the filament pins, and on the grid caps or pins (depending on the tubes).
Regards
Arran