12W air compressor transistor

At signal input levels below 20mW, National Semiconductor's LM378 op amp directly provides current loads of up to 100mA through a 5Ω resistor. Above this level, the booster transistor is biased by the load current to increase the output power. The transistor and op amp have enough heat sinks from the "audio manual book" National Semiconductor Corporation, Santa Clara, California, USA , 1977, CA, 1977, p442-4-43.