I have Octave MRE130 mono amps. See:
OCTAVE Audio
This amp can use EL34, 6550, KT88, KT120 & KT150 tubes. Using KT120 or KT150 tubes will change the sound but it will not result in more power. Right now I'm using KT120 tubes.
I have been thinking about changing the KT120 for KT88 (PSVANE T...