Structure of Vacuum Tubes
An electron tube is a device that utilizes discharge phenomena in vacuum or thin gas therefore, it is also widely referred to as
an “electrovacuum device.” I mainly consists of key components such as the cathode (which receives electrons), the anode (which
emits electrons), the gate (which controls electrons), core columns, and glass tubes
Other components refer to those structural components that have not been manufactured during the assemblyprocess, such as gallium, anode, mica sheets, casing,etc.The componentis a structural element composed of two or moreother parts, such as a loaded tube core, a beam screen, and so on. The combination of other parts and components into avaluable structure is called a device, such as a finished electronic tube.
II. Characteristics of Electronic TubeProduction
Compared with other industrial production, vacuum tube manufacturing has many unique characteristics.
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(I) Broadly Covering Technologies
I. Vacuum technology 2. Glass technology 3. Mechanical technology
4.Chemical Technology 5. Radio Technology6. Metallurgical Technology
(ii) Diverse Materials
(1) Metal materials: tungsten, molybdenum, copper, nickel, iron, mercury, zirconium, titanium, etc, as well astungsten, mercury and nickel and manganese, chrome copper, ferronickel and cobalt alloys, and process compositematerials such as nickel plating, gold plating, silver plating, zircosity spraying, turquoise spraying and carbon spraying.
2.Chemical materials alcohol, butyl acetate, sodium hydroxide, barium nitrate, acetone, nitrocellulose, etc
- Insulating materials: mica, ceramics, bakelite, quartz, and glass, etc.
- Industrial gases: hydrogen, oxygen, nitrogen, natural gas, water vapor, purified compressed air,etc.
(3) Good Vacuum Environment
Electrodes must be highly cdean during manufacturing; this is the primary condition for ensuring product quality. Especially in
cathode fabrication and assembly areas, dust levels are high, requiring employees to strictly follow vacuum hygiene protocols such as
hand washing, changing clothes, removing shoes, and wearing hats.
IV. Purpose and method of cladding of electronic tube materials and other parts
mica sheets, etc., their purpose is
(1) In the manufacture of electronic tubes, a layer of other substances is often covered with the material or other parts after processing, such as cathode and anode. - Changes the radiative properties of another surface
- Altering the electron emission capacity of another surface
- Changes the conductivity of another surface
- Prevent the corrosion of other metal parts
- Changes in the thermal conductivity of the material
- Others
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In addition to the above, in order to improve the vacuum of the electronic tube, many other substances are covered with other substances to achieve the absorption tube in use.
The purpose of the gas.
(2) Types and methods of cladding - mechanical coating method: a spraying method b drawing method c impregnation method d melting spraying method e melting drawing method (hot coating method) f melting impregnation method
G rolling method
2, physical coating method: a cathode sputtering method b vacuum evaporation method
3, chemical coating method: a chemical solvent method b oxidation method c carbonization method
4, electrochemical coating method: a electroplating method b electrophoresis method
V. CMOS
The cathode is the most important element in an electronic tube, the work of the entire tube depends on its characteristics, and its life is also determined by the working period of the cathode.
It was determined that the cathode, which was the source of electron emission, was often considered to be the heart of the electron tube. Electron tubes are emitted using hot electrons, and hot electrons
The emission cathode can be divided into three categories, namely, pure metal cathode, membrane cathode and semiconductor cathode.
A pure metal cathode mainly refers to a tungsten cathode. This is due to tungsten’s high melting point, small evaporation rate, stable electron emission, ability to resist positive ion bombardment and simple manufacturing. Its biggest disadvantage is low efficiency and is mainly used in large power oscillating tubes. The membrane cathode mainly refers to the social tungsten cathode. Like pure metal cathodes, it is heated directly and simple to manufacture. Its disadvantage is that the evaporation rate of 1 needle is large, limiting the improvement of the application temperature, and the emission efficiency is limited.
2 is highly sensitive to gases.
The three filaments are fragile and prone to breaking.
The Dawn Electronic Tube Factory currently uses tungsten cathodes that have undergone carbonization treatment. Compared to tungsten needles, these cathodes have numerous advantages, including higher emission efficiency.
It exhibits stable performance, is resistant to positive ion bombardment, and is not overly sensitive to gases.
The semiconductor cathode primarily refers to the oxide cathode. Its advantages include a low surface emission work function, significantly higher emission efficiency compared to tungsten cathodes and thoriated tungsten cathodes, high current density, relatively low operating temperatures. However, its manufacturing process is complex, typically requiring an external heating device such as a filament. Environmental temperature, humidity, vacuum hygiene requirements are stringent, making it widely used in receiving amplifiers and small-power oscillator tubes.
VI. The Gate
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The grid is responsible for controlling the flow of electrons within an electron tube. Its structure is typically in the form of a lattice or mesh. The grid is a crucial component of an electron tube. It must possess high mechanical strength, as otherwise, variations in the distance between the grid and the cathode or changes in the pitch of the grid can lead to significant changes in the tube’s characteristic transconductance or amplification factor. Additionally, after the electron tube is subjected to oscillation, it can generate microtones and other noises. An unclean grid can also cause back-grid and ionic currents.
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VII. Anode
In electron tubes, the anode serves as a component that receives electrons. As a result, due to the impact of high-speed electrons and the thermal radiation from the cathode and grid, the anode often operates at elevated temperatures. Therefore, designing the anode structure and selecting the anode material become particularly important. The anode must be able to withstand sufficient dissipation power.
The heat dissipation of electron tube anodes can be categorized into two main types: natural cooling and forced cooling. High-power tubes employ various cooling methods such as water cooling, air cooling, oil cooling, and additional heat dissipation devices. The receiving and amplifying tubes all have oxide cathodes. For these types of electron tube anodes, natural cooling methods are generally employed, with certain requirements.
The maximum operating temperature should not exceed 400-500°C to prevent overheating of the cathode. - The lead-out tube is a sealed device, yet its operation requires electrical connections with the outside world. To achieve this, lead-out wires are always sealed onto the tube’s casing (i.e., the core rod section) to extend internal electrodes outside the tube, allowing them to connect with external circuits. There are several types of lead-out wires:
(1) Three sections of wiring: nickel wire, DuPont wire, and copper wire.
(3) Single-section leads: tungsten rods or molybdenum rods.
(2) The second section wiring: tungsten rod (or molybdenum rod) with a twisted copper wire.
Du Meisi – a nickel wire.
(4) Special-shaped leads: In electronic tubes, to address issues related to high-voltage resistance and electrical leakage, the leads are sometimes separated.
In some types of electron tubes, the gate or anode leads are often connected from the top or side of the glass envelope.
KT88-Z - Absorbent agents
Electronic tubes generally require a high degree of vacuum, such as a pressure of 10-4 Pa. Without this, the tubes cannot function properly. However, such high vacuum levels cannot typically be achieved solely through the vacuum system; instead, the assistance of desiccants is often necessary. Therefore, the primary function of desiccants is akin to that of a supplementary vacuum pump, allowing for the enhancement of the vacuum level. Additionally, after the tubes have been sealed, there is often some residual gas present. Furthermore, during operation, components within the tube may also release some gas. All of this gas cannot be expelled from the tube on its own; it can only be removed using desiccants. Desiccants are typically made from barium films, although barium-aluminum and zirconium-aluminum desiccants are also used. - Glass and metal sealing.
In the production of electron tubes, the sealing of glass and metal is a crucial manufacturing process. Apart from requiring mechanical strength, the sealing must also possess excellent vacuum tightness and necessary thermal stability. Materials with extremely close coefficients of expansion for glass and metal must be selected to enable direct sealing of glass and metal, ensuring that the stress within the glass can be controlled within a safe range, thus allowing the glass to function properly.
It will not shatter due to stress.
XI. Electron Tube Mounting Frames and Requirements
The process of assembling electronic tubes involves assembling electronic tube components into an electronic tube according to specifications. This involves arranging filaments, cathodes, grids, beam screens, anodes, and insulating agents onto a mica sheet in sequence, and connecting each electrode accordingly to the core rod’s wire. The requirements include: the cleanliness standards for the assembly process.
Requirements for the integrity of electrode shapes.
Requirements for the accuracy of assembly.
Requirements for secure connection and fixation of additional components.
Requirements for self-inspection and mutual inspection.
Requirements for submission for inspection.
XII. Purpose of sealing and venting
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Sealing an electron tube involves joining the assembled core and the tube casing together. After sealing, the electron tube consists only of the exhaust pipe, which is connected to the external atmosphere for vacuum pumping purposes. During the exhaust process, specified filaments, anode grid voltages, and high-frequency heating are applied to the metal components to decompose and activate the cathode. This process not only removes the gases trapped within the tube and on the surface of the components but also thoroughly clears the gases within the components, ensuring that the electron tube does not release gases from the components during operation, thereby maintaining the vacuum integrity.
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XIII. The Significance and Purpose of Old Training
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Utilize a standard manufacturing process.
The aging process of electronic tubes involves further electrical performance treatment of electronic tubes that have been evacuated, their bases installed, and completed, in order to achieve normal operation.
Its purpose.
Complete the further activation of the cathode to achieve emission within the standard range. Reduce the leakage current between the cathode and the hot filament, as well as between the various electrodes, to stabilize the parameters of the electron tube.
Remove residual gases from the electrodes within the tube to further enhance the vacuum level.
XIV. Testing and Inspection
After the manufacturing of the electron tubes is complete, a series of tests and inspections must be conducted on the finished products to ensure that defective products do not enter the market. The measured items include filament current, anode current, grid current, transconductance, parameter symmetry, short-circuit resistance, and more. During the inspection of the finished products, 100% testing and inspection are conducted immediately after production in the manufacturing workshop. Products that pass the inspection are sent to the quality assurance department, where they are stored for a specified period before the quality assurance department conducts a sample inspection of the tube parameters. Once the inspection is complete, the qualified tubes are stored in the warehouse for a specified period before undergoing further sampling inspections. If there are no anomalies, a finished product certificate is issued, and the products are then stored in the finished goods warehouse.
XV. Life Testing and Special Testing
A vacuum tube is operated under its normal rated conditions until one of its electrical parameters falls to a specified limit. The total duration of this operation is referred to as the tube’s service life. For standard receiving tubes, the guaranteed service life is 500 hours of continuous operation. To ensure the reliability of the service life for tubes leaving the factory, a certain percentage of tubes must be selected from the finished batch for life testing. Such testing not only verifies the operational lifespan but also reveals the suitability of the manufacturing processes and materials used.
In addition to life testing, the factory must also conduct
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Filament continuity testing, thermal stability testing at the glass-to-metal seal interface, etc.
Climate Testing (High/Low Temperature Testing, Humidity Testing, Low-Pressure Testing, Glass Thermal Stability Testing, Tube Base and Cap Secureness Testing)
Mechanical Effect Test
1 Vibration Frequency Test
2 Impact Test
Currently, only the Shuguang Electronic Tube Factory possesses complete lifespan and special testing laboratories to ensure product quality in China.
