This part is a kind of semiconductor called STK443-090.
Function of this product has class AB 3 channels AF power amplifier.
Manufacturers : Sanyo
Image and pinout :
Some of the text within the PDF file :
SPECIFICATIONS STK443-090 1999.08.09 1. Case Outline 18Pins (See attached outline drawing) 2. Function class AB 3 channels AF power amplifier 3. Application 50W audio use 4. Maximum Ratings / Ta 25°C Item Symbol Conditions Power Supply Voltage 1 Vcc max(1) No signal Power Supply Voltage 2 Thermal Resistance Vcc max(2) Signal ,R L=8Ω ,6Ω j-c Per one power TR Junction Temperature Tj max Operating Substrate Temperature Tc max Storage Temperature Tstg Available Time for Load Short-circuit *4 ts Vcc=±35V,RL=6Ω,f=50Hz PO=50W,1ch drive Ratings ±54 ±47 2.2 150 125 30 +125 0.3 Unit V V °C/W °C °C °C s 5. Operating Characteristics TC=25°C,R =6Ω(Non-inductive Load),R =600Ω,V =30dB Item Output Power Conditions *2 Symbol V THD V (Hz) (W) (%) *1 Po1 P [ ... ]