October 1947 Radio-Craft
[Table of Contents]
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Craft,
published 1929 - 1953. All copyrights are hereby acknowledged.
Occasionally when I post a Bell
Telephone Laboratories (aka Bell Labs) promotion from a vintage electronics magazine,
someone writes to challenge the claim being made by Bell Labs of having been the
progenitor of the idea. This full-page ad apparently claiming to have developed
the process needed to grow high purity crystals appeared in a 1947 issue of
Radio-Craft magazine. The huge EDT (Ethylene
Diamine Tartrate) crystal shown was created over a three-month period. Its intended
use was for filters in telephone communications circuits. Development of the crystal
growing process is yet another case of "necessity being the mother of invention," given
that the massive increase in demand for phone service across the country left the
company short on filter crystals. Bell Telephone Laboratories' manufacturing arm,
Western Electric, assumed the responsibility of crystal production as part of their
telephone handset and switching stations component effort.
Bell Telephone Laboratories EDT Crystals
A Crystal that grew from a seed ... The
large crystal in the foreground is an EDT (Ethylene
Diamine Tartrate) crystal. It started from a seed (a piece of mother crystal)
and in three months grew in a slowly cooling solution to the size shown. The small
plate is cut from a large crystal, then gold-plated for electrical connection and
mounted in vacuum. Cultivated EDT crystals can do the same job as quartz in separating
the nearly 500 conversations carried by a coaxial circuit.
Crystals for Conversations
At war's end, the Bell System began to build many more Long Distance coaxial
circuits. Hundreds of telephone calls can be carried by each of these because of
electric wave filters, which guide each conversation along its assigned frequency
channel. Key to these filters was their frequency-sensitive plates of quartz.
But there was not enough suitable quartz available to build all the filters needed.
Bell Telephone Laboratories scientists met the emergency with cultivated crystals.
Years of research enabled them to write the prescription at once - a crystal which
is grown in a laboratory, and which replaces quartz in these channel filters.
Now Western Electric, manufacturing unit of the Bell System, is growing crystals
by the thousands. Many more Long Distance telephone circuits, in urgent demand,
can be built, because the scientists of Bell Telephone Laboratories had studied
the physics and chemistry of artificial crystals.
Bell Telephone Laboratories
Exploring and Inventing, Devising and Perfecting, for Continued Improvements
and Economies in Telephone Service
Posted December 4, 2020