|Note 1) Open Filaments means, the filaments and the grid are longer than the Plate, and stick out on both ends for about 5...8mm. The cold ends of the filaments do not have a very good function, and cause distortion. The AD100 does not use this part of the tube, and the emitted electrons by the cold ends, will bypass the Plate, and land on the glass. At maximum Power this may cause fluorescent, blue glow on the tube glass inside. See also our Tech Brief on Blue Glow in Tubes.
Note 2) Hard-metal filaments are operated at much higher temperature than normal tubes. This tube will glow bright orange, instead of the dark orange color of nickel filament tubes.
Note 3) Individual Test data, are on the Certificate that comes with each individual Tube. Each tube is numbered, inside the bulb with a metal Tag
Note4) Driver tubes. It pays off to drive the AD100 with a tube like AD1, or AV8, because these tubes have the same harmonic distortion spectrum. When the driver tube is operated in the same way as the AD100, the 2nd harmonics will be partially cancelled between the two tubes. You will find more about this in circuit design books. (for instance: R. zur Linde: "Verstärker in Röhrentechnik". ISBN Nr: 3-928051-02-4)
Tube pictures with courtesy of VT-Components