The Mazda AC/Pen, introduced in 1930 on the B5 base, was the first technically successful indirectly-heated power pentode capable of enough output to drive a moving-coil loudspeaker at good volume. The B7 based version followed in 1933.
SeeAC/Pen for more details and AC/Pen for an example of the B5 based version with a black anode.
The electrodes are assembled in a jig and later matched up to the pinch. Here the electrode supports fit into tubes embedded in the pinch. The bright anode is held with four struts that descend to a collar around the pinch stem. This collar has a nut and bolt to allow it to be tightened around the glass tube.
The inner grids are held on one side only.
The Type designation and makers name are etched into the top of the glass envelope. This is one of the early AC/Pen's to be made.
The focus here is on the lettering.
The balloon envelope is 57 mm in diameter and, excluding the B5 base pins, is 115 mm tall.
References: Datasheet, private communication & 1043. Type AC/Pen was first introduced in 1930.