The tube at left, branded "80" by Arcturus is really a 5W4G tube put on a 4 pin base. A correctly marked Arcturus 5W4G is shown at center with a real type 80 at the right for comparison.
I had always thought that this was simply an odd-sized type 80, but a sharp-eyed fellow collector noticed a faint "5W4G" in an octagon on his example. I checked mine, and found the same thing.
The 5W4G is not a good replacement for a type 80, since the 5W4G provides a maximum current of only 300mA versus 400mA for a type 80.