You're welcome. It baffled me for awhile.
If the Nova is like the Decco and has an obnoxiously bright LED under the center of the tube socket you can put a couple of drops of fingernail polish on the LED to tone it down or change the color. The Decco has a bright yellow LED which looks nothing like the real glow of a tube but I put two coats of dark red polish on it, waiting for the first one to dry before applying the second, and the result is a much nicer, soft orange.
I swapped the tube in the Decco for a Telefunken 7DJ8/PCC88, which works fine, but I can't honestly say I can hear much difference between it and the stock tube. Since the 7DJ8/PCC88 tubes work just as well as the 6DJ8, and they're often easier to find at reasonable prices, you might consider them for tube rolling.