Regarding the manufacture of electronic tubes, because I am not a professional, I only know a little about it. I will offer ugliness here and offer it for post-meal talks.
The manufacture of electronic tubes is quite a subject, involving many aspects of physics, chemistry, etc. The knowledge contained therein is very broad. Here, the ice sticks will briefly talk about the manufacture of electronic tubes from the two aspects of material preparation and tube assembly. problem.
First of all, there are materials to be manufactured. Most of the tubes used are high-purity metal materials and various inorganic and organic raw materials. In the appendix of the RCA manual R-13, RCA has proudly introduced some tubes Complex technology. Materials science is a complex subject. I can only say a few sentences. The following uses a simple bypass heat pipe as an example. You can think of it as 6P1 or 6A2.
Material preparation
1. Hot wire preparation:
Using a mixed liquid of nitrocellulose, butanol and ethyl acetate, add fine and pure corundum powder to grind to form a suspension (formulation of American Raytheon Company).
Pure tungsten wire or molybdenum wire is sprayed on the surface by spraying a layer of diaspore suspension, and then heated at 900 degrees for a few minutes and naturally cooled. Then boil the hot wire in 20% potassium hydroxide solution for a few minutes, then rinse and dry with distilled water, heat to 100 degrees in the air for a few minutes, and evaporate the solvent. Then heat it in a high-temperature hydrogen furnace at a high temperature of 1600-1650 degrees for a few minutes, and you can use it.
2. Cathode preparation:
Using a mixed liquid of nitrocellulose, butanol, and ethyl acetate, barium carbonate, strontium carbonate, and calcium carbonate are added, and ground in a ball mill for 7 hours (recipe of American Raytheon Company).
Spray or brush on a nickel cylinder.
3. Electrode preparation:
According to the materials used in the calculation, such as the nickel sheet for the screen electrode or aluminum-coated iron, etc., it is pre-appropriately blackened (as required) and punched into an appropriate shape.
The grid wire is wound on an automatic winding machine (the automatic winding machine has been adopted in the 1920s) to form a grid. The wire used for the grid and the winding process are extremely strict, especially the diameter and spacing of the grid wire of the high-transconductance wide-band voltage amplifier tube are very very small
(The grid wire of the common medium amplification factor transistor is about 0.00009 inches, the high amplification factor tube is smaller, and the diameter of the grid wire of the wide-band voltage amplification tube is more than an order of magnitude. Some cottage factories can only manufacture 205 101 and other old models, they can not make other tubes).
According to the calculation, the mica pieces are cut into a certain shape.
According to the calculation, prepare the appropriate glass bulb and stem.
The metal material is chemically cleaned, and then subjected to hydrogen burning treatment, and the metal that reacts with hydrogen at high temperature is subjected to high temperature treatment in a vacuum furnace.
Die assembly
The different raw materials are assembled on the stem, the spot welding process is used, and various methods are used to fix the electrodes. As you can see through the glass, or smash a tube, you can see more clearly.
Exhaust process
1. Equipment:
There is usually a mechanical pump (mostly piston pump + rotary vane pump) as the first stage of pumping. Then there is a multi-stage diffusion pump (oil diffusion pump or mercury diffusion pump) as the secondary pumping, and is equipped with a condenser and a heater, and an ionization gauge for checking the vacuum degree.
2. Process:
Connect the electronic tube and the connector, start the mechanical pump, and the barometer should reach 1/1000 to 1/10000 atmospheres within half an hour. At this time, the ionization gauge can be turned on to measure the vacuum.
Then start the diffusion pump and let the air pressure express to 1/200000 air pressure within half an hour. Then pull down the oven and bake the tube like a toast. The temperature is 450 to 500 degrees. At this time, the vacuum will drop and it will still be pumped down. Simultaneously heat the main condenser. Until the barometer returns to 1/200000 air pressure.
Turn off the oven, and the electronic tube naturally cools to below 100 degrees. At this time, the vacuum gauge should be at about 1/200000 to 1/500000 atmospheres, and the furnace should be pulled up.
Voltage is gradually added to the filament of the electron tube, and the reading of the ionization meter is observed until the filament is around 550 degrees and the barometer is below 1/2000000 atmospheric pressure. The main condenser is cooled with liquid nitrogen, and the filament temperature is measured with a photo pyrometer. It is generally experienced at 900 degrees and 1100 flashes. After a long and complicated process, the oxide cathode has been activated.
Then the getter can be evaporated by induction heating. At this time, the barometer should be below 1/50000000 atmospheric pressure, and the electronic tube is sealed with a gas flame.
At this time, the air extraction system continued to work, and then stopped the injection of liquid nitrogen into the main condenser, and the condenser gradually returned to room temperature. Turn off the heater of the diffusion pump. When the oil temperature of the diffusion pump is within 60 degrees, close the valve from the diffusion pump to the mechanical pump, and then turn off the diffusion pump fan and the mechanical pump.
The quality of the electronic tube manufactured through the above process is certainly extremely excellent, but for the mechanically manufactured electronic tube, it is usually simplified than the above process, mainly when the exhaust part is industrially produced, it is continuous work instead of the above Work intermittently, but their quality is still guaranteed.
It is worth noting that the formulas of different tube manufacturers are not the same, which is why the service life of different tubes will be different. Of course, for large-scale production plants, their tube quality is guaranteed. For the cottage factory, quality is certainly not guaranteed. The RCA company in the United States claims that the vacuum of their electron tubes can reach 1 / 100,000,000,000 atmospheric pressure, which I believe is more reliable. At least the tube of RCA company I met, even the earlier products, the performance is still quite good. And what technical level can the products of Tianjin Shanzhai Factory reach, because I have never used it, and it is unknown here. However, a long time ago, some friends bought the 300B in Tianjin, and there were many examples of damage in a short time.
Here is a description of the problem of blue light inside the tube
There are many reasons for blue light, some are blue light between the electrodes, and some are blue light on the glass shell. Usually, the reason for the blue light between the electrodes is that the potential difference inside the electron tube is too high, resulting in an arc, which is often seen in some power tubes with high operating voltages. Of course, if it is because the vacuum of the electron tube is reduced, the blue light phenomenon between the electrodes will appear, but generally speaking, for the tube whose vacuum is slowly reduced, its getter usually decreases.
There is also a case where blue light appears on the glass shell, which is commonly seen in some transparent glass shell tubes, such as 6P3P 300B. This is caused by the electrode structure. In a well-designed electrode system, stray electrons bombard the glass There are very few cases of the shell, but some tubes have structural problems or assembly problems, and certain electrons will hit the glass shell. In this case, the noise is easy to cause noise and the current characteristics of the tube become Unevenly, in severe cases, for high-power tubes, it will cause the glass bulb potential gradient to change, causing the glass bulb to electrolyze or even burst, so in general, it is normal that there is no blue light on the glass shell.
Some power tubes use the method of carbon injection. One power tube is easy to dissipate heat, and the other is the average shell potential, which will not cause various problems. The blue light of "floating, mysterious ..." that some masters advocate is completely nonsense and has no basis. I especially like the 6P6P tube. Usually I see carbon injection. Upon closer inspection, it can be seen that compared with carbon injection and carbon injection, blue light is much less.
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