Marshall SV20C tube test: 12ax7 vs 5751 in V1

12ax7: stock Marshall ECC83 5751: GE 5-Star***** Tube position: V1 (preamp) Normal: 4 | High: 2 00:00 12ax7 4|2 00:25 5751 4|2 Normal: 6 | High: 4 00:50 12ax7 6|4 01:15 5751 6|4 Normal: 8 | High: 5 01:40 12ax7 8|5 02:05 5751 8|5 Normal: 10 | High: 10 02:30 12ax7 10|10 02:55 5751 10|10