Bell Telephone Laboratories Ad
June 1954 Radio & Television News Article
a given semiconductor compound, the maximum operational speed of a transistor is governed pretty much by its gate
thickness. Capacitance and impurities along with lithography precision and accuracy are the culprits. Shrinking gate sizes and growing crystals with greater purity
has driven operational speeds upward significantly over the years. An equivalent set of issues plagued vacuum tube
development a century ago. The physical spacing of grid elements wrt each other as well as to the cathode and plate
placed an upper limit on amplification bandwidth. As always, judicious study of the underlying causes led to the
development of new designs that, along with improved manufacturing techniques, overcame existing barriers and, also
as always, exposed yet a new set of limiting criteria for conquering. That's the way of science and engineering.
This advertisement from a 1954 edition of Radio & Television News featured breakthrough development by Western
Electric of the 436A vacuum tube for tripling the number of voice calls that could be sent over a single coaxial
of Contents]These articles are scanned and OCRed from old editions of the Radio & Television News magazine.
Here is a list of the Radio & Television News articles
I have already posted. As time permits, I will be glad to scan articles for you. All copyrights (if any) are hereby
See all available vintage Radio & Television
Telephone Laboratories Ad
Splitting Hairs to Speed Calls
coaxial system electron tube amplifies more voices at the same time because of wider frequency band - made possible
by bringing grid and cathode closer together.
Grid is shown above on left. Picture at right, enlarged 15
times, shows how wires are anchored by glass bond. They will not sag despite nearness of red-hot cathode.
To triple the voice-carrying capacity of coaxial cable, Bell Laboratories engineers had to create new amplifying
tubes with the grid placed only two-thirds of a hair's breadth from the cathode. Furthermore, the grid wires had
to be held rigidly in position; one-quarter of a hair's shifting would cut amplification in half.
with their Bell System manufacturing partners at Western Electric, the engineers developed precise optical means
for measuring critical spacing insulators. On a rigid molybdenum grid frame they wound tungsten wire three ten-thousandths
of an inch thick. To prevent the slightest movement they stretched the wire under more tension for its size than
suspension bridge cables, then bonded it to the frame by a new process.
The resulting tube increases coaxial's
capacity from 600 to 1800 simultaneous voices - another example of how Bell Telephone Laboratories research helps
keep your telephone system growing at the lowest possible cost.
Improving telephone service for America provides careers for creative men in
scientific and technical fields
Click on the thumbnail to the right to view the original
436A datasheet that is still on
the Western Electric website.