The CV1179 is an indirectly heated audio output triode. The prototype was the TT4 and the earlier name for the service valve was the NR57 UK Navy designation and this also is present on the paper label.
The inner coating hides the internal structure.
The top mica showing a rectangular cathode tube and the tops of the grid supports.
Using the microscope: the lower mica with rectangular cathode tube and four strands of insulated heater wire. The cathode oxide coating can be seen together with the blackened anode and the grid wires passing flat across the cathode.
The classic envelope is 44 mm in diameter and, excluding the B5 base pins, is 98 mm tall.
