Rvpiano,
I only have a laymans understanding of the topic (triode, pentode and ultraliner mode configurations).
As I understand it you can configure the output circuit of your amp runing pentode tubes at least three ways.
In “triode mode”, the output circuit is configured to bypasses certain elements of the pentode tube, in effect runs the pentode tubes (five elements) as if they were triode tubes (only three elements), resulting in the tube producing less power then it is actually rated for, and resulting in (claimed) a more lush tube-like sound.
In pentode mode, I believe the circuit is wired to take full advantage of the pentode tube elements, producing more power output, and yielding a different sonic profile.
They may be other differences between the two circuits beyond bypassing elements in the tube, in particular how feedback is used in each of these configurations to control or create distortion—someone more technically knowledgeable will have to pipe in to explain feedback and or correct my comments.
There is also ultralinear mode, which is another variation of the output circuit, supposedly yielding yet another sonic signature (I believe ultralinear mode can be utilized with either triode or pentode tubes, as the changes are implemented with respect to how the output transformer is configured in the output circuit....)
At a practical level, my amp has a switch that allows me to run in either mode.
Not all tube amps under discussion in this thread have this feature.
hope that helps.
