General Electric RB-2-4.5 Radiator Tube (ca. 1935-1960)
The General Electric Model RB 2-4.5 diagnostic X-ray tube seen here is very similar to the Model RB-1-4. My best guess is that it was produced sometime between 1935 and 1960 (definitely as late as 1954).
In the photo, the cathode can be seen extending part way into the spherical bulb from the glass arm attached to the right side of the bulb. Being a double focus tube, its cathode incorporates filaments of two different sizes (see photo below right). The tube could be purchased with, or without, a switch that would facilitate the selection of the filament. Such a switch can be seen plugged onto the end of the RB-1-4 radiator tube. Each of the two tungsten filaments is a cylindrical spiral—typical of tubes that employ the Benson line focus principle. For more information about this, see the introduction to Coolidge X-ray Tubes.
As seen in the top photo, the anode extends all the way from outside its glass arm (attached to the left side of the spherical bulb) into the bulb where it terminates near the center. It is almost entirely made of copper with the exception of its tungsten target. The latter can be seen. embedded in the sloped face of the copper block at the right end of the anode.
The "RB" in the model designation referred to the fact that this was a Radiator tube that employed the Benson line focus design. The "2" indicated that one of the filaments produced a fine to medium focus while the "4.5" indicated that the other filament produced a very broad focus. More specifically, these numbers indicated the approximate diameter of the projected focal spots in mm. For some reason, the 1951 GE catalog indicated that the “RB” referred to the tube’s “round bulb.” It didn't.
Quoting a GE catalog from 1951:
"The RB tube enjoys its continued wide popularity because it is comparatively low-priced, stands up well under hard service, operates consistently, and has maximum energy ratings that, while conservative—in the interests of tube life—are comparatively large. Where economy is necessary and where a maximum voltage rating of 100 kvp is sufficient for the type of work to be done, the RB tube represents an unusual value."
Size: ca. 14" long (excluding rod for radiator fins), 3 3/4" bulb diameter
General Electric Catalog. X-ray Supplies and Accessories. 1951.