The 6W2 is a half wave EHT rectifier for use with flyback supplies. The rectifier can be used at frequencies at and above 50 kHz. TV line output stages would operate at much lower frequencies - 10 - 16 kHz.
The envelope also is marked as R12A.
The bell anode is fixed at one end and the cathode to the pinch. One side of the heater connects to the cathode tube.
The thin glass tube envelope is 18 mm in diameter and, excluding the base wires, is 53 mm tall.