Vacuum tubes history: the rise
The introduction of the tetrode and pentode brought revolutionary improvements in performance. As a result the use of vacuum tubes rose dramatically. Thermionic valves were used in radios which by this time were very popular, but also found many other uses.
Of course the vacuum tubes history is intertwined with the history of television. The first television sets available to the public appeared in 1935. Many special tubes were developed for the sole television industry. By the late 1930s many thousands of different types of vacuum tube were being manufactured by a large number of different manufacturers appearing both in the USA and in Europe.
Many of the vacuum tubes introduced in this period have long since disappeared from common use. However there are a few which were very successful remaining in new designs for a long time. One such valve was the 6L6 used in many guitar amplifiers until quite recently. In many ways it was quite revolutionary because it was the first beam tetrode. It used a new technique to overcome the discontinuity in the characteristic of the tetrode caused by electrons bouncing off the anode. Rather than using a suppressor grid it used a new arrangement connected to the screen grid. This tube became so popular that it was later modified for RF applications by giving it a top cap for the anode. This vacuum tube was called the 807 and was widely used in transmitters in the Second World War and afterwards.
Prior to the war all tubes had used special metal or plastic bases attached to the glass envelope to hold the pins. After the war miniaturization and improvements in manufacturing techniques enabled the pins to be mounted into the glass envelope. By doing this much smaller tubes were made and costs were reduced.