The Monoscope tube
The glass of this type of monoscope tube is normally fully painted
in black obscuring the interior. This tube missed that process allowing a clear view of the inside.
Cathodeon Monicon
Brochure
Cathodeon plan drawing of the Monicon Tube
RCA 2F21 monoscope tube data sheet 1946
RCA 2F21 monoscope tube data sheet 1954