High-power vacuum tubes for industrial heating

In analyzing vacuum-tube failures the principal troubles are: 1. seal breakage; 2. short-circuited grid cathode structure due to weak seals or warping of the high-temperature filament; 3. excessive filament temperature causing rapid evaporation of cathode material; 4. overheated anodes with heavy scale formation and premature failure due to anode puncture; 5. excessive grid dissipation resulting in grid distortion; and 6. gassiness due to momentary overload. Fortunately, most of these evils can be corrected easily. There is, however, no cure for excessive filament temperature except getting a tube with sufficient cathode emission so that it will be capable of the job for which it was designed.