The AC4/Pen from Mazda is an audio output beam tetrode from 1937. It has a high mutual conductance of 11.0 mA/V and a single ended output power of 6.9 Watts.
The AC4/Pen offers a greater output than the AC5/Pen. Both were designed for single output valve radio sets.
The anode has holes in the outer walls through which the inner electrodes are visible.
The secondary emission suppression is achieved with the bright beam plate. The screen grid can be seen passing flat across the cathode. On the left can be seen the closer wound control grid.
The top mica components. The beam plates are bridged and connected to the cathode. Below is the control grid heat sink. The identification is present as a feint image on the dome.
Under the microscope the AC4/PEN becomes visible, whereas in natural light all that can be seen is the ingrained dirt on the dome.
The /PE and the first stroke of the N.
The classic envelope is 54 mm in diameter and, excluding the B7 base pins, is 110 mm tall.
Reference: Data-sheet. Type AC4/Pen was first introduced in 1937. See also1937 adverts.
