The CV571 (commercially the 50L6GT) is an audio output beam tetrode and is designed for series heater chain use with a heater current of 150 mA. Essentially the design is modified from the 6V6GT and designed for the same application within broadcast radio receivers.
Through the internal coating the anode is seen to be box like with ribs for added rigidity of the thin sheet metal.
The cathode tube is rectangular.
The anode seen from the side.
The top view gives more detail. The control grid supports are copper and the beam plate tabs are clearly not grid supports.
The wide glass tube envelope is 28 mm in diameter, and excluding the IO base pins is 74 mm tall.
