Your power output tubes (and small signal pre-amp and power amp input & driver stage tubes) had better match in electrical characteristics (gain, mu, etc.). If they don't, your electronics will create more distortion than if they do. Read up on how a tube circuit operates.
Mixing tube brands
I want to mix Two Gold Lion two KT-88 tubes and two Psvane KT-88 tubes to blend the sound. Is this a problem?