I saw them at CAF last month in a new Jolida amp in Greg Beron's room. From what I understand, the new KT150s replace an EL34 so they wouldn't replace a KT120 or 6550 unless the amp is able to use all these tubes.
Perhaps Greg could shed more light on the subject.
The plate dissipation is 70 watts
G2 is 9.0 watts,
Cathode current is 275 ma
Filament current is 1.75 -2 amps
Max plate voltage is 850
Screen is 650 volts
Distortion in class A
400v plate
225 v screen
Overall Harmonic Distortion is similar to 6550 at 14%.
Dimensions
Maximum height ..........................................140mm, approx. 5.52"
Balloon diameter, max ................................60mm, approx. 2.4"
Maximum weight ........................................130g