This part is a kind of semiconductor called 2N491A.

Function of this product has SILICON UNIJUNCTION TRANSISTORS.

Manufacturers : Digitron

Image and pinout :

Some of the text within the PDF file :

2N489(A,B)-2N494(A,B) High-reliability discrete products and engineering services since 1977 SILICON UNIJUNCTION TRANSISTORS FEATURES  Available as “HR” (high reliability) screened per MIL-PRF-19500, JANTX level. Add “HR” suffix to base part number.  Available as non-RoHS (Sn/Pb plating), standard, and as RoHS by adding “-PBF” suffix.  Stable operation over wide temperature range  Low leakage current  Low peak point current  Guaranteed minimum pulse voltage MAXIMUM RATINGS Rating Total RMS Power Dissipation (Unstabilized) Total RMS Power Dissipation (Stabilized) RMS Emitter Current Peak Emitter Current (TJ = 150°C) Emitter Reverse Voltage (TJ = 150°C) Operating Temperature Range Operating Temperature Range (Stabilized) Storage Temperature Range Value 45 [ ... ]

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