With any output tube replacement the bias would have to be re-adjusted. Both the KT120 and 150 have a higher heater current draw. Check with CJ to see if the amp can handle it before trying those tubes.
Note. Don't expect any more power. I have an Octave V110 which is a modified V70se designed to put out an additional 40W. The plate and grid voltages need to me modified to get more power. That said I asked Octave if the KT150 would be OK for the V110 and the owner responded by saying it will work just fine but I will only hear the sonic differences between the KT120 and 150 but get no additional power. In fact he is considering modifying a V80 to use the full potential of the KT150.
Note. Don't expect any more power. I have an Octave V110 which is a modified V70se designed to put out an additional 40W. The plate and grid voltages need to me modified to get more power. That said I asked Octave if the KT150 would be OK for the V110 and the owner responded by saying it will work just fine but I will only hear the sonic differences between the KT120 and 150 but get no additional power. In fact he is considering modifying a V80 to use the full potential of the KT150.