I don't know what WA actually stands for but it indicates a ruggedized tube designed for industrial and military applications. It can be substitued for a 5687, and a 5687 can be substituted for a 5687WA in most audio applications since it will not be subjected to the extreme conditions the WA was designed for.
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This link will take you to a wealth of tube data. Elevick is correct that a circuit designed for the maximum plate-cathode voltage a WA can handle (330V) will exceed the maximum of a non WA (300V). Most circuits are not designed at the maximum operating points but you should check to make sure.