Transistor Museum Photo Gallery Bell Labs Bead Type First Point Contact Transistor

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Photo Essay – Bell Labs Bead Type Point Contact

Developmental Bead Type Point Contact Transistor (Courtesy Terry Hosking)

Photo Essay Commentary

The two transistors shown in the photo above represent early versions of the Bell Labs bead type transistor technology. The unmarked unit on the left is a prototype unit, likely representing the earliest form of this transistor type. The 1689 (on the right) is the more familiar form of the bead type transistor. This particular unit is hand labeled, with a date code of 6-52 (June 1952) on the reverse side. Note the mechanical similarities between the prototype unit and the later 1689 developmental style. The model 1689 was the basis for a variety of reliability and performance tests performed at Bell Labs in an effort to completely characterize the operational specifications for the plastic bead technology. For example, life test studies were conducted on developmental batches of the primary BTL transistor types in the early 1950s – the types studied were M1689 (bead type point contact), M1752 (grown junction), and various cartridge style point contacts (M1729, M1768, M1734, and others) [3]. Surprisingly, the bead type technology did not perform as well as the other transistor types, with higher failure rates after extended usage.

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