Bell Telephone Laboratories - Ethylene Diamine Tartrate Crystals
October 1947 Radio-Craft

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