Space was always the saga in the development of communication equipment for military purpose. In 1939, in the beginning of the WWII engineers working in the laboratories of the RCA in the USA, developed a very simple technique for the manufacturing of small valves intended for use in military equipment giving birth of the miniature valve (a) According to this new technique, the electrodes made of DUMET metal, an alloy of iron/nickel coated with a copper layer, were sealed in the base of the glass bulb and, finally
soldered into a nickel made pins contacts. The correct position of the valve with respect to the socket was found by placing seven pin contacts on a circle equally devided. Since the tubes were extremely light, no special locking sytem was needed; the contact pressure of the springs in the tube socket was sufficient to secure the valve. (b)
In spite of its excellent performance the manufacturing process of the miniature valve was still complex, demanding a great ability of the operators in the production line
During the Korea war, in 1951, endeavours were made to standardize the types of radio valves used in the communciation equipments used by the NATO members - North Atlanctic Treat Organization.The result was the NOVAL technique, a valve with a circle provided with nine pins. This valve was equipped with three-electrode lead-ins like the miniature ones, however, the bulb shape was improved by sealing it in the valve base upwards. The valve rigidity was also improved by resting the springy teeth of mica's plates againsts its walls. (c )
The miniature valve was the forerunner of another type of thermionic device - the NUVISTOR - that would be developed in 1960.

(a) Cross section of the miniture valve type 6SA6, radio frequency pentode.
(b) Two types of miniature valves; on the left type 6AL5, double diode.
(c) Several types of NOVAL valves.