Electrodes in a 'mixer' valve of the pentagrid-converter type are arranged in two groups, which are symmetrical about two axial planes set at an angle to each other. As shown in cross-section, the cathode K and first control grid G form one group, the other consisting of the first screen grid S, the second control grid G1, the second screen grid S1 and the anode A.
Improved pentagrid electrode arrangement
The longitudinal axis of symmetry of each of the groups coincides with the main axis of the bulb. In this way the first screen grid is brought nearer to the second control grid, and the screening between the two control grids G and G1 is made sufficient to prevent any electronic coupling caused by the space charge which forms the 'virtual cathode' of the outer group. The backward drift of slow-moving electrons is intercepted, whilst other inductive effects due to the virtual cathode are minimised.
Philips Lamps, Ltd. (communicated by N V Philips Gloeilampenfabrieken). Application date january 28th, 1942. No. 556461.