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. |
|
|
|
|
