Power tube designations

[lowit]

Does anyone know what characteristics of a tube give it the following designations "hard blue", "meduim green", "soft red"?

[demonufo]

Those mean absolutely nothing to me, and I suspect are gradings imposed by a particular manufacturer, or a tube vendor. You should be able to find all the info you need on their own relevant web pages, but I doubt very much that these gradings will apply to other tube types in the same way.

[lowit]

I agree with what you are saying but take a quartet of Svetlana EL34 tubes for example. I see a price difference between the "medium green" and the "soft red" to be $30.

[demonufo]

Well that's just crazy. I suspect then, what you are seeing is actually a discounted price for inferior tubes.