Handwritten in green ink vertically on glass envelope.
overall: 2 1/8 in x 2 1/4 in x 2 1/4 in
This is a double beam-power tube with a 1 + 6 pin septar base and two pins for the plate extending out the top of the envelope. One pin is larger than the others to provide the pin-one orientation. This is a spare tube for Register Driver S/N 6.