What parameters do you want to check for Dave ? If you want a basic go/no-go tester then almost any of them should do that, provided they're in good working condition and capable of reaching the HT voltage/current you want to work at (even this can be tricky for, say, KT88s, EL509s etc). If, at the other extreme, you want to match valves accurately for both Ia and gm at an operating point of your choice then that's a much bigger deal. Frankly you'll struggle to get a reliable result from any of the vintage testers. There's a very telling account of why that's so here http://www.jacmusic.com/ (click the union flag, click item 6 on the left hand menu, click item 7 on the left hand menu and learn why "... almost any old tube tester has a large potential for indicating complete nonsense results ..." - sad but true). The bottom line is that to learn the truth you either need to take very good care with the maintenance and calibration of your vintage tester, and acccept its inevitable limitations even then. Or you need to bite the bullet and get a modern one with stabilised supplies capable of delivering the full anode current at true DC. If you're into electronics then there's a nice DIY design for such a thing here http://www.vintage-radio.net/forum/showthread.php?t=48853 but it's not a trivial build (if it was then everyone would have one).
One last point - many a serious service engineer will tell you that the best way to test valves is to measure their performance in the piece of equipment where you will use them. This will tell you what you really want to know. You need to be happy to work inside the kit with the power on it, and I wouldn't encourage anyone to do that who wasn't competent. But it can be very informative indeed.
EDIT: Ah. I've just looked up the Coincident Dragon. Are you thinking of testing the 211's ? If so I don't think there's any vintage tester that will get near to doing that. You'll be into home-brew high-voltage rigs like this http://www.antiqueradios.com/forums/viewtopic.php?f=8&t=65140. These are not for the faint-hearted. They can easily kill. I'm afraid you're going to need the help of someone who's done this before.
Cheers VB you have just convinced me to avoid getting a Tube tester! I am WAY out of my depth here so i will find someone who can test them for me. It's just that i seem to be down on volume from one side, is there a way of checking that?
Yup, as Mark says, swapping the valves will tell you if it's them or not. If you swap them one at a time you can even track down which one it is (make careful notes though, it's so easy to get mixed up when they all look the same). If you want to check whether there really is a problem with the amps then you'll need to know the gain on each channel. This should be a straightforward thing for any tech with the right basic equipment to measure. I'd volunteer myself if you were closer. Depending on where you are in Surrey you might get in touch with John Caswell (Wokingham) or Henry Dulat (Leatherhead).