The 6CJ3 is an efficiency diode for American 525 line colour television receivers.
The anode is stitched together with side flanges for heat dissipation. The bright tune is not the cathobe but a cathode support. The cathode is a single white helix that can be seen entering the bottom of the tube. The heater wires run inside this cathode helix.
The front to back dimension of the anode (4.0 mm) is small in relation to its width (20 mm). There is a white coated wire connected to pin 6 that passes helically inside the cathode tube. It looks to be extra insulation between heater and cathode.
The makers details have rubbed off but the octagonal box on the dome suggests an RCA product.
The wide glass tube envelope is 29 mm in diameter, and excluding the B9D base pins is 65 mm tall.
Reference: Data-sheet. Type 6CJ3 was first introduced in 1966.