2N3439

High-voltage NPN silicon planar small-signal transistor housed in a metal TO-39 can, engineered specifically to withstand severe voltage strain without arcing or breakdown in high-voltage line drivers. Equivalents: 2N3440, MJE340 (plastic alternative), NTE194. Real-Life Examples: Gas-discharge Nixie tube display grid drivers, vintage television CRT cathode-drive matrix panels, high-voltage industrial test benches, and offline power supply regulators.