The filament in a directly heated tube serves as both the filament and the cathode, while the filament in an indirectly heated tube is separate from the cathode.

Study Notes

Electron tubes are electronic components with schematic symbols.
There are different schematics for different types of electron tubes.
Electron tubes are classified based on the number of electrodes they contain.
A diode tube is a two-element tube with a plate (anode) and a cathode.
All electron tubes must have a plate and an emitter.
There are two types of cathodes: directly heated and indirectly heated.
The filament in a directly heated tube serves as both the filament and the cathode.
The filament in an indirectly heated tube is separate from the cathode.
Filaments are not counted as electrodes since their function is only to provide heat.
Some schematics omit the filament for simplicity.

Test your knowledge on electron tubes and their schematic symbols with this quiz! Learn about the different types of electron tubes, including diode tubes, and how they are classified based on the number of electrodes they contain. Explore the two types of cathodes - directly heated and indirectly heated - and their functions. See if you can identify the different schematics for electron tubes and understand why filaments are not counted as electrodes. Challenge yourself and see how much you know about electron tubes!