[Rob Quay]

I’m working on a radio for a friend which has Hytron tubes. No identifying marks are obvious. Is there a way to check what they are? I can trace the socket wiring and make a guess as to what they are- unless they’ve been inserted in the wrong place. Suggestions? - Rob

[DaleHCook]

What make and model is it? The service info may have a chassis diagram which will allow you ti identify the tubes.

[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

[David]

If you have  uv light give it a try. David