The Birmingham age-herald., 1922-08-27

stresses that occur along the faces, while the glass wrapping around the edges of the ribbon is called upon to withstand much greater ten sile stresses and gives way. If the edges of the ribbon are sharpened a tight seal results. the reason be- ing that the forces of adhesion De- tween the glass and copper actins along the flat contact faces are suf- ficient to stretch the thin copper at the edge and prevent it's drf wing away when cooled. There is defi- nite relation between the elastic properties of the metal and glass and the angle of edge that can De used for a successful seal.
 By proper shaping of the metal ribbon seals have been successfully made up to very large sizes. some of these are about one inch in wldth and capable of successfully conduct ing current of 150 to 200 amperes-
 Getting Vacuum Difficult.
 One of the greatest difficulties in constructing the 10-kilowatt tube was the problem of exhausting the tube. This was due to the large amount of occluded gas contained by the metal parts of the internal as- sembly. This extended tho period of pumping and at first caused dangerous warping of the internal structure. because of the fact that during the period of pumping the tube clements were maintained at much higher temperature than they were ever called upon to sustain during normal operation.
 The difficulty was overcome by heating the various parts to the highest possible temperature in vacuum furnace before assembly,, and in that manner getting rid of a large amount of the occluded gas. This greatly reduced the time neces- sary for the pumping operations on the tube.
 It Is not geenrally known how suc- cessful these 10-kilowatt tubes have really been. They have been subjected to a series of exhaustive tests in the laboratory, and have recently been tested out at one of the large trans atlantic wireless stations under conditions approximating actual op- eration.
 The officials of the Bell laborato- ries are naturally maintaining a certain amount of reticence regard ing these tests, in compliance with their known policy of not an nouncing anything until success has completely crowned their efforts
 Big 1OO-KiIowatt Tube Described.
 Despite this, however, some of the facts concerning the 100-kilowatt tube can be told, and they are per- haps best described In the words of Mir. Wilson, as follows:
 "The success which had attended the development of a tube of this high power capacity (10 kilowatts) indicated the possibility of construct ing still larger tubes, and 1t was decided to proceed with the develop ment of tube capable of delivering at least 100 kilowatts in the an- tenna.
 "The development proceeded with few minor alterations along the lines of the smaller tube, nominally rated at 10 kilowatts.
 "The plate, which Is made of a piece of seamless copper tubing closed by a copper disk welded into the end. is IA inches long and 3h inches in diameter. The filament is of tungsten and is 6o-1000 of an inch in diameter and 63h inches long. The current required to heat 1t is e1 amperes and the power con- sumed in 1t Is kilowatts.
 The filament leads are of copper rod one-eighth of an inch in diame- ter and are sealed through 1-inch copper disk seals. The grid is of molbydenum and Is wound around three molbydenum supports.
 Difficulties Overcome.
 "rhe handling of the parts of this tube during manufacture presented a task of no mean magnitude, and r, V k rteoI to assist In the glass working. It has been found necessary, for in- stance, to suspend the plate in gim- bals during the making of the tube seal owing to its great weight, and special devices have been made to hold the filament grid assembly in place while 1t is being sealed in otherwise the strains produced by It's weight cause cracking of the seal.
 "The significance of this develop ment in the radio art cannot be over estimated. It makes available tubes in units so large that only very few would be necessary to operate even the largest radio stations now extant, with all the attended flex- ibilfty of operation which accom- panies the use of the vacuum tube
 From the standpoint of wire less telephony the development o1 these high power tubes gives us the possibility of using very much greater amounts of power than have ever been readily available before The filanents in these tubes have been made so large that the elec- tron emission from them will easily
 RESORTS AND TRAVEL