This exhibit is a large magnetically deflected cathode-ray tube. It is unusual in having a B7 base and hessian cover. There are no identification marks on the tube.
The B7 base seems to indicate a product of the late 1930s and early 1940s. It is too large for domestic television of the period and it was possibly made for use as a plan position indicator in a radar installation. The screen face shows no sign of a rectangular mask or any phosphor burns and so a round display is probable.
Looking down on the tube. The final anode connects to the contact on the right and the evacuation tube is on the left. The inside of the bell is coated with colloidal graphite and this acts as the final anode.
Another view.
The junction between colloidal graphite and screen phosphor. The screen is heavily domed to maintain the glass in compression as far as possible.
The B7 base.
The hessian is glued to the glass and probably serves to reduce the glass spread in case of implosion. This is also not found on domestic equipment.
The electron gun.
The neck is 255 mm long.
The screen lacks evidence of a hard service life and so it is possible that this was never used.
The tube was too large to fit into the museum valve studio. The reflection shows me laying on the floor with the conservatory frame behind.
The end window envelope is 34 mm in diameter, and excluding the B7 base pins is 680 mm tall.
