[Ron Ramirez]

If it has a listing of 1942 Philco models then it cannot be from the 1930s, it must be mid to late 1941.

Philco used the 6L6G tube in the 38-116 and 38-690, then not again until the 42-1016 and (I think) 42-1015. Even then it likely had no direct substitute at that time. I doubt that the KT66 was widely available in this country back then (although I could be wrong), and the 5881 may not have been developed yet (again, not certain without some research).