Speaking of the development of 30, it still has a close relationship with RCA. In the 1920s, battery tubes were mainly in the world like 199,109. These tubes have the feature of saving electricity, but their performance is not very good. In this way, in 1931, the RCA company developed a series of electronic tubes with 30, 31, 32, 33, and 34 types of tubes. The power was still saved, but the efficiency was much higher. Among them, 30 electron tubes are widely used as universal tubes, and its use is beyond description.
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30 can be used for regenerative detection, low-frequency amplification, oscillation, rectification, and even high-frequency voltage amplification. For example, the receiving part of the MP-15 communicator uses more than 30 tubes. There are many that are not repeated here.
In 1936, China produced a small number of test tubes, the most important of which was the No. 30 electron tube. However, because it is extremely rare, it is impossible to see the domestically produced 30 tubes. After liberation, China did not produce 30 electronic tubes. In the radio management regulations of 1955, 30 was listed as a controlled electronic tube. Therefore, the application of 30 in our country is decreasing day by day. With the production of new battery tubes in our country, 30 tubes have already launched a historical stage in China in the 1960s.
Here, I attach the RCA R-10 manual, two pages about 30, for your reference.
Regarding the tube shell, let me say a few words: In the picture below, the RCA 30 tube is a hot-air balloon tube, the term is called the S tube; the Feige 30 is a straight barrel glass tube, the term is called the T-tube; the rear tube is The bottle type is developed from S tube and T tube and is called ST tube. The ST tube has better heat dissipation than the T-shaped tube. It uses mica fixed electrode, top mica and tube neck contact. It has good seismic performance and more stable characteristics. Regarding the various manufacturers of electronic tubes, it is by no means a trivial word. If there is time in the future, we will write a detailed article.
At the time of writing, although many people consulted the documents of Japan, the United States and Europe, they were not simply translators. He hopes to be concise and concise, so there are so many omissions, and people do n’t understand foreign languages. 
