This Amplifier is based on the LM12 power OpAmp from National Semicontuctor

LM12CL was at the time a very good power op-amp that could deliver 40W in 8ohm or 80W in 4ohm load with only 0.01% distortion. It had 10A maximum current capability and 60Khz power bandwidth. 

I was using it for bi-amplification of my speakers with a line level crossover.

The amplifier schematic is very similar to that of LM12CL application note available from National Semiconductor's Site.