TRANSMITTER TUBE INVESTIGATION.

Representative transmitter tubes were evaluated for characteristics which may contribute to the generation of spurious spectrum lines down to 90 db below the maximum carrier power output. Specifically, input and output capacitance variations under a variety of stimuli were measured up to a frequency of 1000Hz. Spurious plate current increments from the same stimuli were also determined from the Class A operation of one of the tubes. A total of six transmitting tube types were utilized during the experimental investigation. Of these, five types were Super Power Tetrodes and one type the tube having the highest power capability of the six was a Super Power Triode. All six tube types were subjected to capacitance variation tests under the stimuli of coolant flows filament current and multi-frequency, forced mechanical vibrations. In addition, one tetrode tube type was subjected to all of the above stimuli in a Class A test using a direct measurement of all spurious plate current increments. Under essentially typical transmitter operating conditions 60Hz ac filament voltage and all coolant flows measurements of the input and output capacitance variations as well as the spurious plate current increments on all five tetrode tube types revealed no spurious spectrum lines up to 1000Hz for at least 90 db below the full power output of each tube type. Under similar conditions on the Super Power Triode tube type, filament voltage and coolant flow to all of the courses except the plate coolant course produced no spurious spectrum lines for at least 90 db below the full power output.