Paulsax, Yes there is a lot of approximation. Junction to ambient temp. coefficient often assumes certain size of heatsink on vertical PC board center located in 1 cubic foot of enclosed space. It never happens so designer has to approximate a lot using large design margins. According to Texas Instr. study probability of semiconductor failure rises fast above 100 deg C junction temp.
I would not worry for semiconductors in properly designed electronics as much as for the life of electrolytic caps that is shortened by half for every 10 deg C increase (starting at about 50k hours at 20deg C).
Free air convection inside of audio cabinet is poor because of shelves and often lack of vent holes. Making such holes or even inserting tiny silent microprocessor fan to force air thru the cabinet would help a lot.
I would not worry for semiconductors in properly designed electronics as much as for the life of electrolytic caps that is shortened by half for every 10 deg C increase (starting at about 50k hours at 20deg C).
Free air convection inside of audio cabinet is poor because of shelves and often lack of vent holes. Making such holes or even inserting tiny silent microprocessor fan to force air thru the cabinet would help a lot.