Lieben-Reisz vacuum tube
It consisted of a partially evacuated glass envelope containing 3 electrodes: a heated platinum filament wire (bottom) coated with barium or calcium oxides which released electrons which were attracted to the positively charged anode wire (top), passing through a "grid" made of a perforated metal plate (center). As in the Audion, a small voltage on the grid could control a larger anode current, so the tube could amplify. The inventors claimed a voltage gain of 33. The tube had a small amount of mercury vapor in it, released by the pellet of mercury amalgam in the small U shaped tube on the lower left side, to reduce the high anode voltage of 220 V required when the tube was evacuated.
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