How to do tubes up grade in a AR ref 1 preamp?

Wanted to up grade my preamp with all NOS tube but the original tubes was marked from V1 to V8 respectively to coordinate 8 sockets on the board.
After replaced with all NOS tubes, when cranking up the volume there was a distortion on one speaker.
what is the proper way to replace tubes? Anybody could help?
Thank you,