70 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1951 



means of a series of seals. The inner or vapor seal is of the glass-metal type 

 especially developed for this particular purpose and capable of withstanding 

 considerable hydrostatic pressures. Next in line there is a seal comprising a 

 central brass tube and an external brass member, both vulcanized to rubber, 

 which is joined to the insulating material of the cable. These seals are co- 

 axial in form, the outer member in each case being brazed to the copper tube 

 of the housing or an extension thereof. Finally a closely fitting "core tube" 

 of copper, extending over the cable insulation for a distance of about seven 

 feet, is brazed to an extension of the copper envelope of the housing, filled 

 with vistac and sealed at the distant end by means of a neoprene sleeve joined 

 firmly to the core tube and to the cable insulation. 



The repeater housing and core tube are provided with corrosion protective 

 layers and a bedding for the armor wires, the bedding over the core tube 

 being built up in the form of a taper. The armor is a continuation of the 

 cable armor wires with additional wires interspersed on account of the larger 

 diameter of the repeater. To prevent twisting of the container due to the. 

 unlaying of the armor wires under tension, a second layer of wires with a 

 direction of lay opposite to that of the main armor is employed. The repeater 

 may be armored as part of the cable or it may be armored separately, with 

 a stub on each end, and spliced into the cable. 



The components of the housings and seals, as well as the complete armored 

 housing, have been subjected to exhaustive tests of various sorts. The rubber- 

 brass seal, for instance, was tested for penetration of moisture vapor over 

 long periods of time. Methods of making this seal were checked by tension 

 tests until a uniformly high degree of adhesion was obtained. Armored hous- 

 ings were tested on a laboratory setup in which laying conditions could be 

 simulated by bending the structure under tension and in motion around a six 

 foot diameter drum. 



The Repeater Circuit 



The diameter of the housing had been chosen originally on the assumption 

 that the bulge caused by the repeater should not be more than two or three 

 times the diameter of the cable proper in order to reduce the possibility of 

 over-riding turns on the brake drum during laying. Mechanical tests indi- 

 cated that this diameter was also safe from the standpoint of deformation 

 of the copper envelope during bending. Accordingly, it was required that the 

 repeater structure should be restricted in cross-section so as to fit inside this 

 tube, with as much length as would be needed. 



The problem then became one of packaging the elements involved in a high 

 gain electron tube amplifier in the restricted space available. The method 

 finally adopted is shown in Fig. 3. The completed amplifier consists of an 



