Telefunken red tip

does the body of the tube have a rectangular 'spot' anywhere on it?

something that looks like there may have been a cloth sticker on it at some time?

... there are lots of rumors about the red tip tubes; dunno if any of them are true... medical useage is one of them (more reliable)

From Brent Jessie Web Site (http://www.audiotubes.com/bjtubes.htm)

MATCHED PAIRS 12AU7/ECC82 Telefunken RED TIP ribbed plate, Tektronix SELECTED TUBE MATCHED PAIR diamond mark, VERY RARE!
New Old Stock in white boxes. These are the nearly extinct SELECTED TUBE with the cloth or foil "Selected Tube" label and the red tips. This identifies the tube as having passed intense quality screening for critical applications in Tektronix industrial equipment. Low noise and no microphonics were just two of the attributes to qualify these for exacting test and medical equipment use. These wonderful vintage tubes are vanishing at an alarming rate. A fantastic, long-lived tube with unequalled sound quality. These are hand selected and matched to within 2 percent transconductance. The rib plate are virtually identical to the smooth plate, but audiophiles note that the lower midrange is fuller. Try them and pocket the savings! The cream of the crop, better get some now!

Brent Jesse has the best historical pedigree of tubes around on his site.
He's also a pleasure to talk to.