Printed with silver ink on top of the glass envelope.
Handwritten with silver ink around the glass envelope.
overall: 3 in x 1 1/4 in x 1 1/4 in
This is a pentode tube enclosed in a glass envelope with a loctal base. Pin 5 is missing by design. This tube type was specially designed for long life, originally for use in the Whirlwind project. This is from the Boston Tube Exhibit of 1998, and includes a brief description.