Telefunken 12AX7. They have a reputation and the price to match, but i find in general these valves overrated, the smooth plates 12AX7 have the typical telefunken house sound, pretty, sweet, light, clean, and airy, and in the right place beautiful, but lacking a little in body and warmth and most importantly timbre, apparently they say the rib plate is fuller with more body than the smooth plate, and they sell a little cheaper. Because they have a very distinctive sound they can be very handy in tuning a system. I found they worked brilliantly in my old Convergent audio technology (CAT) mark 2 preamp, just by putting in a single smooth plate 12AX7 in one of the CATs 10 valve positions, without it the preamp was ordinary, that valve just had the correct flavor in the CAT. The rule is you cannot use a full house of telefunkens in any superbly tuned system as with all valve brands, it's always a mix and match scenario. I own telefunken 12AX7s because they are important in my tuning arsenal but generally keep away from buying too many, problem is you must own them to understand them, and that is the key to use them in the right place. Picture of a smooth, then a rib plate Telefunken 12AX7. Always look for the diamond logo between the pins before buying.