General Electric KR-3 Kenotron Tube (ca. 1930s-1950s)

Quoting Grigg's Trail of the Invisible Light: "In 1914, at GE's Research Lab in Schenectady, [Saul] Dushman developed the hot cathode valve tube. This [referring to a photo of the KR-3] is the first commercial model (KR-3). Its long life stemmed, in part, from the fact that the anode surrounded the cathode, thus preventing erratic voltage drops due to charges developed on the inner surface of the glass." 

The label on the stem identifies it as a "Coolidge" tube, but it came to be known as a "kenotron."


The photo to the right show the spiral cathode inside the tubular, open-ended anode.

The KR-3 was air cooled (the KR-4 was oil cooled).

Size:  20" long,  5" in diameter (bulb)

Price: $248 in 1953-1954 GE catalog


E.R.N. Grigg. Trail of the Invisible Light. Charles C Thomas. 1965.

General Electric X-ray Corporation. Coolidge X-ray Tubes - Kenotrons. Bulletin No. 293. 1934.

General Electric Catalog. X-ray Supplies and Accessories. 1953-1954.


Donated by the University of Kansas courtesy of Michael Lemon

Coolidge Type X-Ray Tubes               Museum Directory

Last updated: 06/24/09
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