Smooth plates are just a bit richer. Maybe a bit more "tubey" than the ribbed plates. I am exagerating here to make an example. The differences are not huge, but there. Both excellent. Do you know what a Bugle Boy sounds like? Well the ribbed plate is more like that as opposed to something like a Mullard.
Which Telefunken 12ax7
I'd like to hear from members who are familiar with NOS Telefunken 12ax7s from the 1950&60s. I've spoken with three different tube vendors who are frequently recommended on this forum and received three different assessments of the ribbed vs smooth plate versions. One vendor said there was no sonic difference, while the other two were opposed as to which was warmer and which was more detailed. I sure would appreciate it if you guys could help straighten this out.