The CV3613 (commercially the 6AR6) is a beam tetrode. The design features allow for high peak currents and anode voltages within the dissipation limits. The characteristics required in CRT horizontal timebases.
The box anode has side flanges for additional cooling and to make convenient point for fixing.
Tilted slightly from the above image the lower components are easier to see. The heater is folded to six vertical strands.
The wide glass tube envelope is 35 mm in diameter and, excluding the IO base pins, is 74 mm tall.
