THE BIGGEST VACUUM TUBE
A ONE-HUNDRED-KILOWATT VACUUM power-tube is now in use at station WGY, Schenectady, New York, operated by the General Electric Company. This, it is asserted by the company in a press bulletin, is the first practical use of a tube of this size by any broadcasting station. The tube takes the place of eight 20-kilowatt tubes in WGY’s transmitter, and is five feet tall, and with its water-jacket stands seven and one-half feet high, and weighs 100 pounds. We read:
“With such a tube available, radio engineers will be able to carry on their investigations in broadcasting on higher powers than have heretofore been possible. Up to the present time fifty kilowatts in the antenna has been known as ‘ super power,’ but with tubes of an output of 100 kilowatts at hand, investigations will be possible up to 500 kilowatts, or even more.
“The 100-kilowatt tube is used as a radio amplifier, fulfilling in the transmitter a use comparable with the radio-frequency stages in most radio receivers. In the receiver, a very weak, high-frequency oscillation is picked up by the antenna. This excites the radio-frequency-amplifier tube which amplifies the power or signal. In the transmitter, the output of one 20-kilowatt tube is amplified by the 100-kilowatt tube.
“In the development of the 100-kilowatt tube the vacuum-tube department and research-laboratory engineers had to devise an entirely new structural design to provide necessary strength and durability. Outside of its water-jacket the tube is five feet high, and two-thirds of this height consists of the copper envelop, four inches in diameter. The envelop serves a double purpose, for it not only contains the elements of the tube, but is, itself, the anode or plate of the tube.
“The upper third of the tube is made of glass, through which the filament-leads and the grid-lead find insulated entrance. The glass bulb is twenty-two inches long and four inches in diameter, and it is sealed to the spun-out end of the anode cylinder or copper envelop by a machine-process in such a way as to make the junction of glass and copper mechanically strong and vacuum-tight.
“The grid, within the copper envelop, is cylindrical and has an overall length of three feet five inches. The grid frame is a most ingenious structure of molybdenum and tungsten. Bracing, such as is common in steel-bridge and tower construction, is used in the design to provide maximum strength with a minimum of metal. Sufficient rigidity and strength are necessary in this construction to prevent short-circuiting from swaying or sagging.
“Uniform water-flow around the anode is necessary to prevent unequal heating, and for this purpose a new type of water-jacket has been designed. This consists of an ordinary jacket with an inner flexible jacket to direct the water by the anode.”
Source: The Literary Digest for April 16, 1927