440 BELL SYSTEM TECHNICAL JOURNAL 



amplifier protected the recorders from damage, and the effect of each 

 Hghtning discharge was limited to the possible mutilation of one or 

 two letters. 



The protection of these amplifiers from mechanical vibration has 

 proved entirely satisfactory. During alterations to the Western 

 Union Cable station building at Rockaway Beach a brick wall six 

 feet from the amplifier was broken down with sledge hammers without 

 interfering with the normal handling of messages. 



Other Applications of Vacuum Tube Amplifiers in 

 Cable Telegraphy 



While as yet vacuum tube amplifiers have been utilized principally 

 on high speed loaded cables they are not necessarily restricted to such 

 use. It was mentioned in an early part of this paper that, since the 

 non-loaded cables are ordinarily operated duplex at a speed which is 

 set, not by the sensitivity of the receiver, but by the strength of the 

 interference due to imperfect balance between cables and artificial line, 

 no increase in speed might be expected to result from the substitution 

 of vacuum tube amplifiers for the mechanical amplifiers now used. 

 Nevertheless the superior ruggedness of the vacuum tube amplifier, 

 combined with its ability to operate safely through thunderstorms 

 which would ruin the mechanical amplifiers, might reduce appreciably 

 the amount of lost time, particularly during the summer months, and 

 thus improve the traffic capacity of these cables. 



In addition to the use of vacuum tube amplifiers for operating 

 terminal apparatus they have another important field as repeaters 

 intermediate between two short sections of a long cable. As the speed 

 at which any cable can be operated is roughly inversely proportional 

 to the square of its length, it is customary to lay cables connecting 

 distant centers of population in two or more sections, interrupted at 

 some conveniently located but often inconveniently isolated island. 

 This involves repeating the signals received from one section of the 

 cable into the next section and for years this was done manually, 

 that is, an operator received and translated the signals and passed 

 them on to another operator for transmission on the other section. 

 Within recent years through relay operation by means of repeaters 

 has become general. At the intermediate station a device receives 

 the signal from an amplifier and retransmits it to the next section 

 usually correcting it completely to its original form. These repeaters, 

 while very successful, are still quite complicated mechanically, and 

 require skillful maintenance, particularly as they utilize delicate 

 mechanical amplifiers and moving coil relays. It is possible to replace 



