TRANSISTOR MUSEUM Historic Transistor Photo Gallery
Transistor Size (1/4” Diameter X 1/4”H) Standard T0-5 Case Date Code 104 (1961 Week 4) on 2N491 Date Code 233 (1962 Week 33) on 2N489 Cardboard Box Packaging	GE 2N489 – 2N494 TYPE N-Type Silicon Bar Unijunction Transistor USAGE Timing/Waveforms DATE INTRODUCED 1957 CASE STYLES Blue Metal Top Hat (Early) Black Metal Top Hat (Later) AVAILABILITY Common (High Volume Production)
HISTORIC NOTES General Electric was an industry leader in germanium technology throughout the 1950s. A unique GE semiconductor invention was the unijunction transistor, which was developed at the General Electric Electronics Lab at Syracuse in the early 1950s. Originally known as the “double-base diode”, the unijunction became a very big seller for GE in the late 1950s and into the 1960s. The first high volume commercial unijunction product line was labeled as 2N489 – 2N494, with each of these different types selected for specific switching characteristics. The unijunction transistor differs from all other transistor types in that it has only a single “PN” junction – it also exhibits what is known as “negative resistance”, a characteristic it shares with only a few other unique semiconductor devices such as the tunnel diode and the point contact transistor. GE maintained market dominance for the unijunction for two decades, with TI and Motorola being much smaller second source suppliers. The 2N489-494 line remained relatively expensive, at the $8 range in both the 1960 Lafayette Radio Semiconductor catalog and the 1968 Newark catalog.
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