Up for sale here is this vintage Ken-Rad 6F6G tube.  It has a "W0" date code, for late 1940.  I tested this on my B&K 747B tube tester, and it tested at 60, on a scale of 0-120, where 65 is minimum good, and had no shorts or grid emissions.  This should still have a fair amount of life left.  This is guaranteed to work for you.  Please see my pictures for details.

US shipping and handling is $4, and international is $14.  I accept Paypal.  If you have any questions, please ask.

I have a number of other tubes, collectibles, Magic cards, and vintage electronics listed--feel free to take a look!