This early-production Bose® 901 Active Equalizer came through the shop recently for a repair. These Early models were the very first production run, back in 1968, and have a pretty significantly different circuit design from the later models, and feature a solid hardwood case rather than a particle board case with contact paper on the later models. They’re also a few years older and even more likely to fail, too.
This model uses a single-ended, single-sided board which easily lifts out to access the bottom traces for soldering.
Time for a quick power-on check:
Looks good! This Active Equalizer got a complete overhaul, and now it’s even better than new and will sound fantastic for a long time to come.