Went to Digikey product index
Selected Linear - Audio Amplifiers
Filtered by 16 pin DIP package
Filtered for stereo chips
Filtered for ones that work on more than 5V (input DC went via switch then to IC, not via the 7805)
Downloaded each data sheet one by one and looked for GND on 3,4,12,13 and V+ on 16.
Only one possibility left
Checked where the input and output pins went to see if that made sense with PCB
Posted here
Yes, I have been servicing audio gear for about 35 years.