original early 20th century bulbar focus type medical x-ray tube. found in the collection of a grant hospital radiologist. features aluminum rod anode w/ concave aluminum cathode. round thin target made of platinum. highly collectible and sought after piece of vintage medical equipment. manufactured by the r.f. co. (chicago, il). etched signature reveals part number and maker. these tubes are somewhat similar to the crookes, geissler and holtz tubes manufactured by pressler bros. based in germany.