Sprague 2N128 Transistor  
Written by AnubisTTP on 2022-12-04  



The 2N128 and 2N129, initially released by Philco in 1953, were the first commercially produced surface barrier transistors. Surface barrier transistors make use of an improved manufacturing process, in which jets of indium sulfide were used to erode a germanium die down to a thickness of only a few thousandths of an inch. Indium was then electroplated to each side of the die, resulting in a junction with superior high frequency response to the point contact and alloy junction transistors available at the time. The 2N128 contains a vertically mounted surface barrier die bonded to a three pin base, which is packaged in an pill-shaped TO-24 aluminum enclosure. The example shown here is a second-sourced variant produced by Sprague.

Philco surface barrier transistors were a commercial success, and saw use in a number of historic devices including the UNIVAC LARC supercomputer, the AN/GSQ-33 ground guidance computer for the Atlas ICBM, and the Athena ground guidance computer for the Titan 1 ICBM. Philco surface barrier transistors were also used in Explorer 1, the first satellite launched into orbit by the United States and the third in the world, following the successful launch of Sputnik 1 and Sputnik 2 the prior year by the Soviet Union.


Sprague 2N128 Transistor
Sprague 2N128 surface barrier transistor.

Sprague 2N128 Surface Barrier Transistor
Sprague 2N128 at rest. This part was originally developed by Philco in 1953.

Philco Surface Barrier Transistor Prototype
Prototypes of Philco's surface barrier transistor were mounted in glass electron tube envelopes for testing. None of these devices were ever made available to the public however; commercially released 2N128's are packaged in much more practical TO-24 'pill' enclosures.

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