The M-OV MKT4/5 is a beam tetrode version of the earlier (1932) MPT4 output pentode and was intended as a plug-in replacement, production of the MPT4 being discontinued. The beam tetrode version gave slightly more output power than the pentode but with significantly lower distortion. Whether its performance was any better than that of Mazda's landmark (1930) AC/Pen is open to question!
However, this exhibit is a genuine MKT4 five pin and it has three wire grids. It is not the only example of a MKT4 pentode.
As the MKT4/5 was a plug-in replacement for the MPT4 pentode, the B5 base and side contact for the screen grid was the required configuration. Most MKT4's made were to this pattern. Later M-OV fitted the valve with a B7 base. Looking at the MKT4/7 one can see that the electrode assembly remained unaltered, just the base changed.
In single ended audio configuration would provide an adequate 2.5 Watts.
The side contact is for the screen grid.
This is a beam tetrode and the beam plates appear in this image as feint lines. The inner grids and coated cathode are highlighted. The control grid is wound on copper supports. The cathode tube is a cylinder.
The classic envelope is 45 mm in diameter, and excluding the B5 base pins, is 103 mm tall.
References: Data-sheet & 1040. Type MKT4/5 was first introduced in 1937. See also1937 adverts.
