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. There is a heavy line painted with yellow ink around the circumference at the top of the envelope. This is a spare tube for Register Driver S/N 6.
Printed in white ink around glass envelope.
Handwritten in green ink vertically on glass envelope