General Electric KR-3 and KR-4 Kenotrons

Ref. F1

The first picture is of the air-cooled KR-3, 22” (55 cm) long, the earliest commercially known hot cathode rectifier valve by General Electric, developed by Saul Dushman in 1914, introduced in 1915, and which became commercially available only in 1926 (Grigg, The Trail of the Invisible Light, Charles C. Thomas, 1965, pp.77&98).

The second picture is of the oil-immersed KR-4, 16” (40 cm) long, direct descendent of the KR-3. The two kenotrons are internally similar, with an axial filament on a spiral support inside the cylindrical anode.

No technical specifications are available.