[Arran]

Have you tried putting them in the freezer, sometimes that will make the numbers show up, or by breathing on them. Another way to narrow it down is by looking at the internal structure of each tube, like a 12AV6 is a triode, double diode, and the diodes are in a box bellow the triode, the rectifier will be very simple inside with a flat, black plate, or plates, the power output will have a rectangular plate (usually) and a bigger heater/cathode.
Regards
Arran