The Mazda AC/Pen, introduced in 1930, was the first technically successful indirectly-heated power pentode capable of enough output to drive a moving-coil loudspeaker at good volume. Originally released with a B5 base cap, in 1933 it was also made available with the then brand new B7 base as shown in this exhibit.
This exhibit is a later example with a B7 base and a blackened anode for better cooling. The AC/Pen became a UK industry standard and was widely copied under a variety of names.
The AC/Pen may be found listed under: AC/PEN; ACPen; AC/Pen/5; ACPEN/7, and all possible permutations of these.
To prevent the electrodes moving in the balloon envelope, a collar and vertical supports fixed around the pinch stem are employed.
The Type designation is etched into the dome. inside can be seen the wire grids. To reduce electron emission from the control grid, cooling of the grid is provided by a radiating fin attached to the top supports.
The balloon envelope is 58 mm in diameter and excluding the B5 base pins, is 116 mm tall.
References: Data-sheet & 1043. Type AC/Pen was first introduced in 1930. See also1930 adverts.
