Popular Science, November, 1922, page 43:
     The  World's  Most  Powerful  Tube     
W. G. Housekeeper and 100 kilowatt vacuum tube PERFECTION of the most powerful vacuum tube in the world--the 100-kilowatt giant just produced by engineers of the Bell laboratories--is undoubtedly the outstanding radio development of the month. One of these tubes would be sufficient to maintain constant wireless telegraph communication across the Atlantic Ocean, while four of them, joined in parallel at the gigantic transatlantic wireless stations, should permit continuous telephone conversations between New York and European capitals under all conditions.

Difficult  Problems  Solved

    At first glance, it may not seem remarkable that such a powerful tube should have been developed, but experience has demonstrated that when the output of an ordinary vacuum tube is extended beyond one kilowatt, a series of practical difficulties arises, and among them are the problems of cooling the tube so that it can be kept in continuous operation, and also of maintaining the vacuum.
    In the new tube, these difficulties have been overcome. The metal has been sealed to the glass, so that a variation in temperature ranging from that of liquid air to more than 300 degrees above zero, Centigrade, fails to sever their connection, or break down the vacuum of the tube.
    Another unique feature is the system of water cooling. The plate of the tube is on the outside of the glass, but sealed to it. It is the long, dark-colored metal cylinder shown in the above photograph. In use, this plate rests in a deep socket, where water is circulated to keep the huge tube cool. Grid and filament are inside this cylindrical plate.
    Not only does this new development offer immediate opportunity to bring about reliable transatlantic telephone conversation, but it brings the day nearer when we may replace with such tubes the ponderous and costly alternators now used for long-distance wireless communication and those used for power transmission, as well.