CHAPTER FIVE - Electron Tubes and Devices

Abstract

This chapter discusses electron tubes and devices. With small receiving tubes with oxide-coated cathodes, low heater voltages should be avoided as much as high heater voltages. Some types of tubes with tungsten or thoriated tungsten filaments, large rectifier types, gas-filled and vapor-filled types require a close control on filament or heater voltage. Measurement of the heater or filament voltages should be done by connecting the voltmeter directly to the tube pins or terminals, thus avoiding voltage drop errors in the filament supply leads. The waveform of the supply should also be substantially sinusoidal. Small receiving types operated in parallel from the electricity supply mains give satisfactory operation if the voltages on the heaters and filaments are within ± 5.0 % of the rated value when the supply voltage is at its declared value. Allowance is made for the 6 % mains voltage variations above or below the declared voltage permitted by the electricity supply regulations.