This series of plastic, medium-power NPN transistors are designed for use as audio amplifiers and drivers utilizing complementary or quasi complementary circuits.

Features
• DC Current Gain − hFE = 40 (Min) at IC = 0.15 Adc
• BD 135, 137, 139 are complementary with BD 136, 138, 140.

WHAT IS AUDIO AMPLIFIER ?

An audio amplifier is an electronic component that amplifies low-power audio signal to a level which is suitable to drive a loudspeaker or any high volume speaker.