This part is a kind of semiconductor called 2N3899.

Function of this product has SILICON CONTROLLED RECTIFIER.

Manufacturers : Digitron Semiconductors

Image and pinout :

Some of the text within the PDF file :

High-reliability discrete products and engineering services since 1977 2N3870-2N1850, 2N3896-2N3899, 2N6171-2N6174 SILICON CONTROLLED RECTIFIER 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. MAXIMUM RATINGS Rating Symbol Value Unit Peak repetitive forward or reverse blocking voltage (1) (TJ = -40 to 100°C, ½ sine wave, 50-400 Hz, gate open) 2N3870, 2N3896, 2N6171 2N3871, 2N3897, 2N6172 2N3872, 2N3898, 2N6173 2N3873, 2N3899, 2N6174 VRRM or VDRM 100 200 400 600 Volts Peak non-repetitive forward or reverse blocking voltage (t ≤ 5ms) 2N3870, 2N3896, 2N6171 2N3871, 2N3897, 2N6172 2N3872, 2N3898, 2N6 [ ... ]

2N3899 PDF Datasheet Download