Printed in gray ink on the circumference of the envelope.
Printed in white ink in two lines around the base of the tube.
S 1768 C
Printed around the base in white ink inside a square that contains a large letter 'A'; the '1768' is below the horizontal bar of the 'A' and the other two letters are outside the top of the 'A' but inside the square.
overall: 5 in x 1 1/8 in x 1 1/8 in
This is an electron tube with a bakelite 8-pin octal base.