What is the characteristic of diff. Triode Tubes?

Before delving into the subjective differences in the three named tubes it might benefit us to answer the first question which is what are the characteristics of the three tubes. The 300B and 2A3 are true triodes or three element tubes, without getting too technical they consist of a cathode, a plate and a control grid between the two. When operated single ended the inherent distortion signature of these tubes is that distortion, although high, diminishes linearly as the harmonics of the fundamental increase. The KT-88 is a different beast. It is a beam power tube. A beam power tube is a pentode or five element tube; the elements are the cathode, control grid, screen grid, plate and supressor grid. The additional elements are used to collect and concentrate stray electrons flowing from the cathode to the plate into beams thus substantially increasing efficiency but, some would say, adversely affecting the distortion spectra of the tube. Such a tube, the 6550 is a similar power tube, can be operated without using the additional elements and then can be said to be a pentode tube operating as a triode. One problem with this is that the additional elements are still in the physical envelope of the tube and certainly affect the path of the electrodes from cathode to plate and are two more elements to resonate causing distortion. Although many would argue that the the distortion spectra of a pentode is subjectively improved by only connecting the three elements many also believe the the distortion spectra is still several orders of magnatude less consonant with the musical structure than true triodes.

Just to confuse matters my above description is of the 6550 the KT-88 is a kinkless tetrode but behaves the same way.