I will probably go with the 12b4 as I have a pair. To run them in Guinevere you need a second socket is they are single triode's. Add 1 or 2 more LED's to the string and crank up the current a bit, that's it. I bet there are some folkes more familiar with the world of 9 pin tubes, that can recomend a low mu twin that you can pretty much pop right in...John