I was retubing some amplifiers this past weekend. I was installing some NEW JJ and EH 12AX7 tubes. I was running all the tubes through my Jackson 658 tube testor. I always sort tubes to find those with closely matched triodes for the phase inverter positions. All the tubes were good, but I was noticing a fair discrepancy between both halves of the same tube. Some tubes were spot on matches (most of the EH), but some of the JJ's varied as much as 105-87. I realize that's within a 20% tolerance, but I rather expected them to be a bit closer. I have noticed that the GT12AX7M tubes tend to be within 10 from one side of the tube to the other. Good NOS tubes vary even less. Have others had similar experiences? I was retubing a tweed Bassman clone. The amp uses each half of the V1 tube for a separate channel(normal and bright). The 20% difference does make a noticeable difference in gain between the normal and bright channels.