[Synchrodyne]

No. The VHF valves at interest were special tetrodes, designed to minimize partition noise. This was done by aligning the grids so that the screen grid was shadowed by the control grid. This minimized screen current. In the case of the 30F27, the normal screen current was just 10% of anode current. For comparison, the EF183, a frame-grid remote cutoff VHF pentode of the same era had a normal screen current that was 35% of anode current. The smaller proportion of the cathode current that is going to the screen, the less effect fluctuations in that current have on anode current.

The designers of those VHF tetrodes would have had as an objective getting the partition noise as low as they reasonably could, well below that of pentodes and not too far above that of triodes. Otherwise they would not have had much of a case against the emerging crop of triodes, which were getting easier to neutralize.

That said, if one stands back it could be said that in the realm of receiving valves at the time, none of the tetrodes were what might be called conventional. The audio, video, field and line output tetrodes were all of the beam tetrode type, with aligned grids and kink-minimizing geometry. Aligned grids were sometimes use with output pentodes, an example being the PL84/UL84/EL86 group, where it might have been a necessity to keep the cathode current within a manageable limit.

I suppose that a VHF pentode might have been designed like these VHF tetrodes with, aligned grids and low screen current. But presumably the designers felt that their tetrodes were adequately kink-free such that there was little benefit to adding a suppressor grid. And whilst cascode performance was a reference point, the tetrode would have to be competitive in first cost with the new triodes, which of course had but one grid.


Cheers,