I had this tube in my small collection and I decided to play a little bit with it. The tube was given to me, and I didn't know if it was in working state. For the moment I just wanted to make it glow, so the first thing I did was to check the filament with a multimeter in continuity (and resistance) mode.
The meter beeped and it measured a low resistance value so the filament was ok. The filament specs are 2.5V/5A, so I adjusted the power supply...
connected the tube...
Et voila...
Cetron 3B28 tube glowing
So the filament was ok, and it produced a nice, warm light!