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 a spare tube for Register Driver S/N 6.
Date
1948 ca.
Manufacturer
Sylvania
Place Manufactured
U. S.
Identifying Numbers
Model number
7AK7
Printed in silver ink on the top of the glass envelope.