Uses or function of vacuum tube in the circuit?

Answer 1

The simplest answer to that question is: Vacuum tubes were originally used to

perform every function now handled by transistors.

The transistor was a big improvement over the vacuum tube because in order

to perform those functions, a vacuum tube needs two power supplies, including

one at a comparitively high voltage, it occupies a comparitively ridiculous amount

of space, and radiates a comparitively ridiculous amount of heat.

When vacuum tubes were still the only way to go, there were no portable radios

smaller than a Chicago phone-book, and most of their weight was made up of

several heavy batteries.

Answer 2

Vacuum tubes are used in electronic circuits to amplify signals, switch circuits on or off, and generate or process electrical signals. They were commonly used in audio amplifiers, early radio receivers, and analog computers before semiconductor devices like transistors became more popular due to their smaller size and lower power consumption.