. The Bell System technical journal . Fig. 33—Cross section of a 721A TR Tube, showing the special shape of the temperature compensated discs The life of a TR box is in general determined by the gas volume. Theradio-frequency discharge consumes no gas except at extremely high powerlevels; the igniter discharge accounts for the greater part of the loss of thegas initially placed in the tube. Reduction of the water vapor to hydrogenby formation of copper oxide on copper parts of the tube seems to be theprincipal process which goes on. This change results in no change in totalpressure until the w
. The Bell System technical journal . Fig. 33—Cross section of a 721A TR Tube, showing the special shape of the temperature compensated discs The life of a TR box is in general determined by the gas volume. Theradio-frequency discharge consumes no gas except at extremely high powerlevels; the igniter discharge accounts for the greater part of the loss of thegas initially placed in the tube. Reduction of the water vapor to hydrogenby formation of copper oxide on copper parts of the tube seems to be theprincipal process which goes on. This change results in no change in totalpressure until the water vapor is exhausted; thereafter sputtering becomesmore important and accounts for a fairly rapid hydrogen clean-up. Thelife of a TR tube is determined by the igniter current, which is maintainedat a value as small as possible consistent with adequate spike protection, andby the volume of the tube. 86 BELL SYSTEM TECHNICAL JOURNAL. u. GAS-DISCHARGE TRANSMIT-RECEIVE SWITCH 87 The lack of water vapor in a tube which has been operated for somehundreds of hours may manifest itself by a failure in either protection orrecover) time. The operating frequency determines which failure becomesimportant first; at long wavelength it is likely to be recovery, while at shorterwavelength the spike protection is likely to fail first. The life of a TR tube operated without igniter is ver> much longer. Thismay be understood from the picture given above under recovery, of thestate of affairs existing in the radio-frequency discharge. Electrons do notcompletely traverse the gap, but oscillate about some mean position, whilethe positive ions hardly move at all. Thus there is little more interactionbetween the metal electrodes and the gas molecules with the dischargeon than with it ofif. A few 721As have been operated without igniter foras long as 5000 hours with no measurable change in either protection or re-covery. This exp
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