This double triode is equivalent to the ECC81. The device was designed for RF use and is of the low impedance type. The lettering was probably all orange once with the heat of operation causing the colour change.
The anodes have been folded from single sheets and stitched together.
The anodes are separated by 6 mm and are less than 2 mm thick.
The thin glass tube envelope is 21 mm in diameter and excluding B9A base pins the length is 47 mm.
References: Datasheet & 1040. Type 12AT7 was first introduced in 1947.