[Phlogiston]

Another important tube testing note:

Most tube testers (all I have used) do not use enough plate voltage to properly test eye tubes.

First, the test is rather arbitrary requiring the user to evaluate "brightness". To do this you almost need a NIB tube to compare to.

Generally a tube that generates light bright enough to see in both the open AND closed settings in a well lit room will be quite usable in a radio at higher plate voltages.

This is still a good test though. You will be aware of tubes that have had a lot of use. But since most radios are not "daily drivers" an old tube my be good enough.

Conclusion is to test marginal eye tubes in a radio.