A valve or vacuum tube is a main component of early-day electronic items, whereas today we use transistors. However, it is a large component compared to the transistor, and it must use two separate voltage lines to power up. It is made from a complete vacuum bulb. It has three main electrodes as anode, cathode, grid and filament electrodes:
For Valve, it must use two separate voltages,
Low tension (L. T) -Low voltage(L. T – about 6.3V) with high current used for the filament.
High tension (H. T) – High voltage(H. T – 90 – 300V) with low current used for anode, cathode & grids.
There are several types of valves – such as Diode, Triode, tetrode, pentode etc.
Symbol of valves
anatomy of valve.
Diode valve specially use for rectification. Working principal of diode valve.
Filament – Here filament is used as a heater.
Cathode – cathode is put as near as possible to filament and cathode connected with the negative H.T supply. So, when it heats the filament, the cathode also gets heat, and it will emit those electrons on it. Since the valve has vacuum space, it can freely emit electrons. However, those electrons are naturally negatively charged, so it will be attractive to the anode which is always connected to the positive H.T supply.
Anode – Connected with positive H.T supply, so it will attract free electrons as it is positively charged.
Diode valve only have anode, cathode and filament, Triode and others have grid.
Triode valve – Triode work same as a diode valve beside it use grid there between anode and cathode.
Grid -It uses, between cathode and anode as a coil grid or as a spiral. So it can control the flow of electrons using grid voltages which are going through cathode and anode. Like if grid have negative current, it will oppose some electrons and reduce the flow of electrons to the anode. But with a positive current, it will attract more electrons. Thus, it will increase the electron flow to the anode. It’s much like using a water tap between pipes to control water flow.
For find pins which connected to inside you must refer valve datasheets. Valve are usually fitted with valve bases.