After a 24 hour burn in all power tubes are tested for noise and matched at multiple operating points for plate current (± one milliamp) and transconductance.
The JJ KT88 is a modern replacement for all classic KT88 applications. They can also be used in place of 6550's when space allows. Tonally these tubes sound exactly like they look, huge!
As with the original GEC's, the JJ KT88's can develop 50 watts per tube in the right push-pull applications (Ampeg, Hiwatt, Sound City).
If you're considering these as a 6550 replacement, We recommend a minimum of 2-1/4" as measured from center to center between the sockets for adequate ventilation.
Please leave us a note in the comments section as to what amp they're going into and or if you're looking for a specific grade.