I like the look of that! How many watts is it roughly?

Wow! thats very cool! congrats on getting a working hot cathode tube! I too am quite curious what its voltage drop is? (i assume your driving it at the same current a 38W 2D is which is about 430Ma...) what Phosphors did you use btw? if you dont mind me asking, how did ya (re)activate the cathodes and avoid contamination?

Impressive!

The voltage drop is 43v, although i said its not contaminated, its developed an odd characteristic, if the fillaments are heated, they release contamination but the tube cleans up once it strikes. So it cold starts fine but once you use a starter it wont work till it cools.

I used a variable power supply to activate the cathodes with the vacuum pump valve wide open to remove any gases released. The fillaments were yellow hot.

interesting quite a low Voltage drop for such a relatively thin and long tube I wonder if the buffer gas pressure is low?... doing some quick maths (assuming running on 50Hz mag gear) gives me 15W , i wonder what would happen if you rehooked it up to the vacuum gear and heated the cathodes while pumping it back down, then pumped it back up much like bombardment during a neon tubes manufacture, edit: oh cool (just saw the comment you posted while i wrote this one) strange that they still release contamination during normal operation... maybe they need longer? I assume during normal operation they are being run at 430Ma?