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Siemens & Halske tube type OR From the collection of the Technical University, Delft, The Netherlands Photo by, Adri de Keijzer

Siemens & Halske tube type OR This is a Space Charge (two grid) tube from the early 1920 's. From the "Taschenbuch der drahtlosen Telegraphie und Telephonie" by F. Banneitz, issued 1927. I have the following data: OR = Telefunken RE 87. Oxid filament 2.5V at 1.1A . Sp. Ch. grid  80V, Anode 220V, slope 7 to 10 mA/V, Durchgriff 4% (mu = 25). Ia 100mA (I suppose this is the saturation current). This particular tube has 380 hours of operation, as indicated on the label at the socket. The photo was made in July 2000, using a Nikon Coolpix 950 (2.1M pixel)