The 6463 is a double triode designed for use in computer circuits. It will maintain emission after long periods in the cut-off state and is of special quality construction designed to withstand vibration and has a long working life.
Like other valves designed for computer applications it is not rated for use in circuits where hum, noise or microphany could be a problem. Certainly not an audio valve.
The General Electric branding. The valve has significant heater power and the anodes are larger than would be found in small signal valves like the ECC8x series.
The side view. The grid of the left hand tower can be seen through the hole in the anode.
The thin glass tube envelope is 20 mm in diameter, and excluding the B9A base pins is 59 mm tall.
Reference: Data-sheet. Type 6463 was first introduced in 1958.