What OT primary for KT88 SE?

[tubeswell]

From what I understand

gm = transconductance (change in the plate/cathode current divided by the corresponding change in the grid/cathode voltage, with a constant plate/cathode voltage.)

mu = amplification (the gain of the stage)

rp (or ra) = plate resistance (the internal impedance of the plate - which increases proportionally with increasing current, at any given bias voltage)