[Hammarlund] Re: 6C4WA compatibility.

[Gerry]

The WA at the end of the tube type designation indicates a ruggedized
version of a standard tube. You should be able to substitute a 6C4WA where a
6C4 was used but not necessarily vice versa. In other words, where there is
a 6C4WA, you may not be able to substitute a 6C4. I have heard this is true
in the R-390 but cannot confirm it as I don't have my R-390 working yet.

Gerry