Crack Analysis, Glass-Ceramic Insulator of Vacuum Tube

摘要

The high voltage glass-ceramic insulators from ten vacuum tubes that had failed a bubble leak test were analyzed to determine the cause. All insulators exhibited a similar crack pattern. It appeared that the primary crack initiated at a point near the top of the insulator and resulted in a fracture that radiated from the inner sleeve of the tube to the outer frame. These cracks were duplicated on subassemblies by applying heat to the inner sleeve near the top surface of the insulator. It was determined that the cracks resulted from heating problems associated with the source closure braze. It was determined that misalignment of the radio-frequency braze coil caused cracking of assemblies. (ERA citation 05:032704)