Water-Cooled Tubes

Radio Record, Volume II, Issue 14, 19 October 1928, Unnumbered Page

Water-Cooled Tubes

The Principle Described

LIE water-cooled tubes used in the highpower stages at 2YA are somewhat of a mystery to many people, as they cannot understand how it is,that water can be used at all. The photograph. shows three of the tubes in question and gives a good idea as to how the cooling is accomplished, The construction of the tubes differs from that of the ordinary receiving tubes, in so far as the plate is not sealed inside the glass, but is welded to the glass and in actual contact with che air. (Continued on page 2.)

The plate is a cylinder of copper shaped like an elongated sewing thimble (but much larger), and is fixed to the glass bulb by means of a vacuum tight weld. The junction between the copper plate and the glass bulb can be seen in the photograph at the lower end of the glass portion. The purpose of the glass is merely to support the grid and filament which extend downwards into the inside of the plate and cannot be seen in the photo. The vacuum is, therefore, inside the plate. not the plate inside the vacuum as in the usual types. WHEN inserting « tube in its receptacle, the plate, which is fitted with a clamping flange, is lowered into the water-jacket as shown and clamped tight. Water is forced round the outside of the plate by means of a circulating pump, and the temperature of the plate is kept at a safe value. As the water is actually in contact with the plate, which is also at a potential of 10,000 volts, it is necessary to provide against electrical leakage. This is accomplished by using a good gerade of water (for pure water is not a conductor of electricity, as many people think), and connecting a long coil of rubber horse between the water mains and the tube. When it is considered that the plate current of each tube is over 500 milliamperes at 10.000 volts and that the filaments each require over 40 amperes at 24 volts. some idea may be gained of the amount of heat required to be carried away by the water.