Design and Analysis of Filament Power Supply Method for Increasing Life Time of Thermal Emission Tubes

This paper has reviewed power supply methods for thermal electron tubes and proposes a method for purpose of increasing its lifetime, with reducing complexity of circuit and, improvement in power efficiency. In this work, the filament is operated with a decreased voltage level while maintaining the output anode power at the same level as required for the filament's operation at nominal voltage. The supply circuit is designed to avoid the reduction of filament voltage below a minimum level. A power converter made of thyristors and rectification diodes is designed to supply the filament voltage. Converter is carefully monitored and controlled by an algorithm embedded in a contemporary Digital Signal Processor (DSP). Filament voltage is gradually changed in a ramp form to minimize surge currents that may lead to decrease the lifetime of the filament. Filament current is continuously monitored to detect the surges. Ramp up/down speed of filament voltage is reduced to its half at the presence of a surge. In this approach, screen grid of the electron tube is maintained at a constant potential while anode and Radio Frequency (RF) input to the control grid are controlled by the proposed algorithm to achieve the expected anode output power. The possibility of implementing such an algorithm has been tested with a RF amplifier working in class C mode. Here some of the corresponding practical parameters are also discussed. Finally, filament supply power converter and its rectifier have been studied and, results are analyzed.