HOW TO CLEAN VACUUM TUBES

Vacuum means a space without anything in it i.e. a space that is devoid of all. Vacuum tubes revolutionized the world of electronics in the year 1904 when they were first developed by John Ambrose Fleming. Vacuum tubes are essentially a glass tube that has all the gas removed from it. In fact, it is safe to say that the branch of electronics started with the introduction of vacuum tubes. Vacuum tubes are also known as electron tube or valve.  Electron tubes such as cathode ray tubes (CRT) were used in TVs for enhancing the display.  Vacuum tubes were initially used as switches and amplifiers in various computers and audio devices.

Vacuum tubes control the flow of electrons in a vacuum. Since there is no gas inside the tube it ensures transparency. Vacuum tubes contain electrodes which control the electron flow.  Vacuum tubes do the basic job of converting an alternating current in to direct current. Although semiconductor devices have taken over most of the vacuum devices they still play an important role in the field of nanotechnology.

John Ambrose’s vacuum tube:

The tube consists of an anode and a cathode in a vacuum environment. Most tubes that you will see around normally are generally made of glass or aluminum and are cylindrical in shape and not more than six inches tall.

The basic concept in a vacuum tube is the Edison effect. Thermionic emission is the concept in which the filament heats up in the vacuum because of the current and at the right temperature the electrons are emitted and cross over to the positively charged plate thus completing the circuit. In John’s vacuum tube the current flows only in one direction and these have been used to make diodes and logic gates which convert the AC to DC power.

There are many other kinds of vacuum tubes and these include

  • Diodes
  • Triodes
  • Tetrode Pentode
  • Magnetrons

Triodes have been used as amplifiers which have been helpful in the development of the oscillator. Oscillators bought about a change in how sound comes out of the radios. They are used to filter and amplify the signals which have played an important role in improving the function of clocks, television transmission, microwaves, radars and computers and many more things.  Vacuum tubes are the reason that you could see the video images on your TV.

What is inside the tube?

Cleaning the vacuum tubes is a very delicate business and therefore it is very important that you understand what is inside the tubes that are there on your devices. Only one scientist Lee De Forest invented the Audion Vacuum tube which was similar to the original tube however it could amplify the signal much more sensitively which lead to the first loudspeaker in 1921. The Audion has an added electrode which forms a grid.  In the Audion a heated cathode produces the electrons that when passing through the grid (or many) and then strike the anode place where they are absorbed. This means that the small AC signal is converted into larger AC signal. A typical vacuum tube is a glass bulb with wires passing through its bottom which connect to the grid and electrodes inside. There are many shapes and sizes of vacuum tubes. As the users are expected to change the tubes themselves they are designed in the plug and play design.

  • Cathode:

    There are two different types of cathodes that are used. One is the thoriated filament which works like a light bulb but it has a very rare metal Thorium added to it. When heated to a temperature of about 2400 degree Celsius thorium makes better electrons then basic tungsten. The benefit is that the thoriated filaments last long and work well with high voltages. The second type of cathode is the oxide coated cathode also called the filament. This oxide coated filaments heat up at only 1000 degree Celsius and emits better electron than the thoriated filament. This oxide filament is generally used in small tubes. The life of the cathode tubes largely depends on the type of material that is used in the cathode. Impure cathodes are what that causes the tubes to wear out quickly.

  • Tube life:

    This is a very important factor to remember when cleaning the vacuum tubes. If the tube is not operated at proper temperature then it will shorten the lifespan of the tube. Dirt and particles on the tube can make it difficult to operate properly and thus shorten the life of the tube. If you operate the tube too hot it will shorten its life and if you operate it too cool it will shorten its life. It has been suggested what operating the tube 20% below the suggested voltage is the ideal way to increase the life. If operated well a good quality tube can last for up to one lac hours or more.

  • The anode or Plate:

    The plate receives the electrons and then transmits the output. The anode plate can get hot and therefore a proper cooling method is needed. There are two ways to do it one is to design the plate to cool itself out by radiating heat through the glass or use liquid or forced air for cooling purposes.

  • The Grid:

    The control grid is generally a simple piece of plated wire. The wire plating is generally gold and the posts are made of soft copper. Since they have to handle a lot of heat they are made of tough metals like tungsten or molybdenum. A tube which has only one grid is called the triode. Specially designed triodes can be used in pulsed radars and other physics work where there is a requirement of energy physics work.

If you add another grid to the triode then it becomes the tetrode. This works on the principle of Miller effect.  Large ceramic tetrodes are generally referred to as the beam tetrodes.  The pentode is the diode with three grids. The third grid is called the suppressor grid.  There are more tubes with different kinds of grids but are no longer in production.

  • The heater: the cathode does not heat itself and has to be at a very high temperature to emit electrons. This heater has to heat the cathode but not get too hot itself otherwise it will burn out. The heater is coated with aluminum oxide and insulation and does not touch the cathode.
  • The getter: The essence of the vacuum tube is the getter. This ensures that the vacuum lasts for as long as possible. If there are any leaks in the tube it will not function properly. The getter can remove the stray gases left in the tube. The getter has a shape of a small cup and can react to and absorb even the tiniest bit of oxygen. The getter is the small silvery patch that you see inside the glass tube. If the seal of the tube is faulty then the getter will turn white.

Although the tubes were becoming obsolete for some time they are very reliable in amplifying and there they are making comeback in the form of specialized tubes. Vacuum tubes are used in High power RF applications because they are cost effective. They are used in guitar amps because of the excellent tone that they produce. This is because of the properties of beam tetrode or pentode amp which lets them have the kind of distortion that is needed and the speaker damping characteristics. Professional audio studies use tubes in microphones, preamplifiers, limiters, equalizers etc. to get the desired sound output.  High-end audio systems use vacuum tubes to give the users excellent listening experience.

 

Tips For Clean The Vacuum Tubes:

It is easy to understand how to clean the vacuum tubes if you understand the parts and delicate nature of the parts. Therefore you have to be very careful when cleaning the vacuum tubes that you have. If you have been hearing a crackling or humming sound when using the tube then there is a chance that the tube needs cleaning.

Clean the pins: Pins are something that most people miss when cleaning the tubes whereas they are the first thing which you should clean when working with the tubes.  In case of stainless steel pins, you can notice that there can be some corrosion in the pins.  Dust, oil impurities are the most common reasons that can cause the pins to function incorrectly. As electrons flow through these pins the release impurities which cling to the pins. Copper sulfate and Iron Oxide and the two most common types of impurities that can prevent making a good connection especially in low voltage conditions hampering the electron flow. Tools that you will need to clean the pins:

  1. Microfiber towel
  2. An exactor knife with a thin blade.
  3. Old toothbrush
  4. Eyeglass cleaner

Hold the tube gently in your hands in the microfiber towel and then using the knife gently scrape the pins clean by using upward motions. You will notice the change in the color of the pins immediately. You can get the oxidation removed comfortably this way. Once you have removed the oxidation take the toothbrush and spray some eyeglass cleaner on it. Give the pins a nice cleaning. Make sure that you keep the microfiber towel close and tight at all times. Alternatively, you can also use a q tip and dip it in the cleaner and clean the tips of the tubes.  Do not use rubbing alcohol too because they are not a friend of the tubes.

If you have the practice you can also use a small sandpaper to gently clean the tips. As a home remedy, some have claimed that even diluted lemon juice works well in cleaning the pins.

Be careful how you handle the vacuum tubes:

The tubes do not like to have contact with oils and dirt and fingerprints from the hands. These kinds of things cause them to get hotter than necessary and shortening their life. Always use a paper towel, microfiber towel or lint-free cloth to hold the tube.  Do not try to touch the hot tubes always turn the component off and wait for it to cool down a few minutes. Do not try to pry out the tube from the socket. Use gently and firm motion to pull it out. You need to clean the socket too and you can do it by removing the pins and putting them back in to get them cleaned.

Cleaning the glass:

There are details printed on the glass which you do not want to be wiped off therefore if you get any prints or marks on the glass then gently wipe the tube with a slightly damp lint-free cloth. Be very careful if you notice that the print is coming off then stop immediately. Once you wipe the print away its gone completely and trust us you don’t want that.

Vacuum tubes can be your prized procession if you are an audio buff. They can help you produce sounds with a quality which you will not get with modern devices. Therefore take care of the tubes, understand how they work and how you can clean them to give them a long and full life.

 

 

 

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