“4UD” Therapy Tube by General Electric

Ref. C4

Dating probably to the late twenties or early thirties, the Coolidge type deep therapy tube is 32”(80 cm) long with a 8”(20 cm) bulb.

It has a large two-inch (5 cm) tungsten anode disc with a relatively low target angle of 30 degrees compared to the 45 degrees in early Coolidge type tubes.

Its technical specifications remain unknown.

Note the peculiar cathode with a small rod-like protrusion from the center of the flat, slightly convex, concentric helical filament, probably intended to help shaping the flow of the electron beam towards the anode. Note also the brownish hemispheric discoloration of the tube bulb facing the anode disc.