What is the advantage of directly heated cathodes?

Hot cathodes typically achieve much higher power density than cold cathodes, emitting significantly more electrons from the same surface area. Cold cathodes rely on field electron emission or secondary electron emission from positive ion bombardment, and do not require heating.

What are the different types of vacuum tubes?

There are many different types of vacuum tubes, most of which fall into four general types: (1) The diode, (2) the triode, (3) the tetrode, and (4) the pentode. Of these, the diode is used almost exclusively for changing ac current to dc current.

How does a triode work?

In the triode, electrons are released into the tube from the metal cathode by heating it, a process called thermionic emission. The grid acts like a gate for the electrons. A more negative voltage on the grid will repel more of the electrons, so fewer get through to the anode, reducing the anode current.

What countries make vacuum tubes?

Vacuum tubes are made on an industrial scale only in China, Russia and Slovakia.

What is the principal advantage of an indirectly heated cathode over a directly heated cathode?

(c) Advantages of indirectly heated cathode: – Eliminates the unwanted a.c. noise associated with the directly heated cathode on account of varying voltage drop along filament length. – Better electron emission efficiency due to improved surface area characteristics.

Which metal is used mainly in thermionic generator in the case of indirect heating method?

Caesium is employed because it is the most easily ionized of all stable elements. A thermionic generator is like a cyclic heat engine and its maximum efficiency is limited by Carnot’s law.

What does GT mean on a vacuum tube?

“G” means a glass version of a metal octal tube, typically in a larger bulb with shoulders. “GT” means a glass tubular version of a metal octal tube.

Why did we stop using vacuum tubes?

Vacuum tubes suffered a slow death during the 1950s and ’60s thanks to the invention of the transistor—specifically, the ability to mass-produce transistors by chemically engraving, or etching, pieces of silicon. Transistors were smaller, cheaper, and longer lasting.

What is electronic triode?

Triode, electron tube consisting of three electrodes—cathode filament, anode plate, and control grid—mounted in an evacuated metal or glass container. It has been used as an amplifier for both audio and radio signals, as an oscillator, and in electronic circuits.

What is electronic thyristor?

A thyristor is a four-layer device with alternating P-type and N-type semiconductors (P-N-P-N). The primary function of a thyristor is to control electric power and current by acting as a switch.

Is anyone still making vacuum tubes?

Current audio vacuum tube production is still largely limited to 3 locations: China, Russia and the Czech and Slovak Republics. While many other developed nations still produce and develop vacuum based electronics, only Japan and Germany have produced glass vacuum tubes suitable for audio recently.

Does anyone still make vacuum tubes?

Three of the most widely available newly produced vacuum tubes are made by JJ Electronics, Valve Art (O&J Enterprises), and Ruby Tubes (Shuguang Electron Group). They are all over Amazon.com and eBay at reasonable prices.

What’s the difference between direct and indirect heating?

On the other hand, indirect heating technology does not allow the product to come in contact with air or gas or any other heating agent to change the final temperature. Indirect heat transfer uses conduction, radiation or convection to achieve temperature change.

What are the disadvantages of indirect fired heaters?

Some negative aspects about indirect fired heaters are: Higher Cost – The rental cost is nearly quadruple that of direct fired Lower Efficiency – Fuel efficiency is usually close to 80% Electricity Required – Indirect fired heaters always need an electrical outlet

What kind of Technology is used for indirect heat transfer?

Indirect heat transfer uses conduction, radiation or convection to achieve temperature change. There are various types of technologies used in both the direct and indirect heating of bulk solids.

How does an indirect heat exchanger work?

A series of vertically stacked modules filled with hollow, stainless steel plates comprise an indirect heat exchanger. This unit uses a counter-current flow of heating water or fluid running through the hollow plates to achieve indirect heat transfer through conduction.